codeforces 1077A

#include<bits/stdc++.h>
using namespace std;
int main()
{
    vector<int>v;
    long long int a,b,k,t,d,e,ans;
    cin>>t;
    while(t--)
    {
         ans=0;
        cin>>a>>b>>k;
        d=k/2;
        e=k-d;
        ans=(e*a)-(d*b);
        cout<<ans<<endl;

    }
}