#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include <iomanip>
using namespace std;

int main(){
    int n, l, r, a, b, ans;
    cin >> n;
    for (int i = 0; i < n; i++){
        cin >> l >> r >> a >> b;
        ans = max(l*a, r*a) + b;
        cout << ans << endl;
    }
}