#include <iostream>
#include <vector>
#include <iomanip>
#include <algorithm>
#include <map>
#include <cmath>
#include <bitset>
#include <string>
#include <queue>
#include <stack>
#include <set>
#include <tuple>
#include <atcoder/all>
#include <sstream> // std::stringstream
#include <regex>
using namespace atcoder;
//using mint = modint998244353;
using mint = modint1000000007;
using namespace std;
using ll = long long;
static const double pi = 3.141592653589793;
const int INF = (1<<29);
const ll mod = 998244353;

int main() {
    int t;cin >> t;
    while(t--){
        int l,r,a,b;
        cin >> l >> r >> a >> b;
        cout << max(a*l+b,a*r+b) << endl;
    }
}