#include<bits/stdc++.h>
#define ll long long
using namespace  std;
int main()
{ 
    ll t;
    cin>>t;
    while(t--){
        ll n,d;
        ll a,b;
        cin>>n>>d>>a>>b;
        ll mult,sub,sub1,mult1;
        mult=n*a;
        sub=a-b;
        sub1=n-d;
        mult1=sub*sub1;
        
        cout<<mult-mult1<<endl;
    }
}