#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <utility>
#include <bitset>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cstdio>

using namespace std;

int main() {
    int t;
    cin >> t;

    int L, R, A, B;
    while (t--) {
        cin >> L >> R >> A >> B;
        if (A >= 0) {
            cout << A * R + B << endl;
        } else {
            cout << A * L + B << endl;
        }
    }
    return 0;
}