#include <bits/stdc++.h>
#include <atcoder/all>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n, m) for (int i = (int)(n); i > (int)(m); i--)
using namespace atcoder;
using ll = long long;
const ll MOD1 = 1000000007LL;
const ll MOD2 = 998244353LL;
using namespace std;
const vector<pair<int, int>> dpos4 = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
// const vector<pair<int, int>> dpos8 = {{-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1, 1}};
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;
}


int main() {
    int 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;
    }
	return 0;
}