#include<bits/stdc++.h>
#include<atcoder/all>
#include<string>
#include<vector>
#include<algorithm>
#include<map>
#include<math.h>
#include<set>
#include<regex>
#include<deque>
#include<queue>
#define all(x) x.begin(),x.end()
#define gall(x) x.begin(),x.end(),greater<>()
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define pb push_back
#define ll long long 
#define P pair<int,int>
#define LP pair<ll,ll>
using namespace std;
using namespace atcoder;


int main(){
int t; cin>>t;
rep(i,t){
   ll ans=0;
   ll l,r,a,b; cin>>l>>r>>a>>b;
   if(a>=0) ans=r*a+b;
   else ans=l*a+b;
    cout<<ans<<endl;
}




return 0;
}