#include <stdio.h>

int main(void)
{
    int T = 0;
    scanf("%d", &T);
    int ans[T];
    for(int i = 0; i < T; i++)
    {
        int L[T], R[T], A[T], B[T];
        scanf("%d %d %d %d", &L[i], &R[i], &A[i], &B[i]);
        if(A[i] <= 0)
        {
            ans[i] = A[i] * L[i] + B[i];
        }
        else
        {
            ans[i] = A[i] * R[i] + B[i];
        }
    }
    for(int i = 0; i < T; i++)
    {
        printf("%d\n", ans[i]);
    }
    return 0;
}