#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>


typedef long long int ll;
//#include<bits/stdc++.h>


using namespace std;



int main()
{

    int Q;
    Q = 1;
    cin >> Q;

    while (Q--) {

        int ans = -1e9;
        int l, r, a, b;
        cin >> l >> r >> a >> b;
        for (int i = l; i <= r; i++) {
            ans = max(ans, a * i + b);
        }
        cout << ans << endl;

        

    }

    return 0;
}