#include <bits/stdc++.h> 
#include <atcoder/all>

#define pub push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (ll i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (ll i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
using namespace std;
using ll = long long;
using Pll = pair<ll, ll>;


using namespace atcoder;
using mint = modint998244353;
using mint2 = modint1000000007;

constexpr long long INF = (1LL << 60);
constexpr double EPS = 1e-9;
constexpr double PI = 3.141592653589;


template <typename T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;  // aをbで更新
        return true;
    }
    return false;
}

template <typename T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;  // aをbで更新
        return true;
    }
    return false;
}

template <typename T>
T sq(T x) {
    return x * x;
}

std::string zfill(int n, const int width)
{
    std::stringstream ss;
    ss << std::setw(width) << std::setfill('0') << n;
    return ss.str();
}


//多倍長整数を(string→vector)に変換
vector<ll> digit(string s) {
    ll n = s.size();
    vector<ll> d(n);
    rep(i, n) {
        d[i] = s[i] - '0';
    }
    return d;
}


//多倍長整数の足し算
vector<ll> adds(vector<ll> s, vector<ll> t) {
    ll n = s.size();
    ll m = t.size();
    if (n > m) { swap(s, t); n = s.size(); m = t.size(); }
    reverse(ALL(s));
    reverse(ALL(t));
    rep(i, m - n) {
        s.pub(0);
    }
    bool kuriage = false;
    rep(i, m) {
        ll a = s[i];
        ll b = t[i];
        ll c = a + b;
        if (kuriage) {
            c++;
        }
        if (c >= 10) {
            c -= 10; kuriage = true;
        }
        else {
            kuriage = false;
        }
        t[i] = c;
    }
    if (kuriage) {
        t.pub(1);
    }
    reverse(ALL(t));
    return t;
}


vector<ll> carry_and_fix(vector<ll> digit) {
    int N = digit.size();

    for (int i = 0; i < N - 1; ++i) {
        // 繰り上がり処理 (K は繰り上がりの回数)
        if (digit[i] >= 10) {
            int K = digit[i] / 10;
            digit[i] -= K * 10;
            digit[i + 1] += K;
        }
        // 繰り下がり処理 (K は繰り下がりの回数)
        if (digit[i] < 0) {
            int K = (-digit[i] - 1) / 10 + 1;
            digit[i] += K * 10;
            digit[i + 1] -= K;
        }
    }
    // 一番上の桁が 10 以上なら、桁数を増やすことを繰り返す
    while (digit.back() >= 10) {
        int K = digit.back() / 10;
        digit.back() -= K * 10;
        digit.push_back(K);
    }
    // 1 桁の「0」以外なら、一番上の桁の 0 (リーディング・ゼロ) を消す
    while (digit.size() >= 2 && digit.back() == 0) {
        digit.pop_back();
    }
    reverse(ALL(digit));
    return digit;
}


//多倍長整数の掛け算(s × t) 計算量は N(|s||t|)?
vector<ll> mul(vector<ll> s, vector<ll> t) {
    reverse(ALL(s));
    reverse(ALL(t));
    ll NA = s.size();
    ll NB = t.size();
    vector<ll> res(NA + NB - 1);
    for (int i = 0; i < NA; ++i) {
        for (int j = 0; j < NB; ++j) {
            res[i + j] += s[i] * t[j];
        }
    }
    return carry_and_fix(res);
}


/*  make_is_prime(N)
    入力：整数 N
    出力：N までの数字が素数か判定したベクトル（i番目がtrueならiは素数）
    計算量：O(nloglogn)
*/
vector< bool > prime_table(int n) {
    vector< bool > prime(n + 1, true);
    if (n >= 0) prime[0] = false;
    if (n >= 1) prime[1] = false;
    for (int i = 2; i * i <= n; i++) {
        if (!prime[i]) continue;
        for (int j = i + i; j <= n; j += i) {
            prime[j] = false;
        }
    }
    return prime;
}

int main() {
    //cout << fixed << setprecision(10);
    ll t; cin >> t;
    rep(i, t) {
        ll l, r, a, b; cin >> l >> r >> a >> b;
        cout << max(l * a + b, r * a + b) << endl;
    }
}