#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    long long n, a, b;
    cin >> a >> b >> n;
    if (n % 2 == 0)
      cout << (n / 2) * (a - b) << endl;
    else
      cout << ((n / 2) * (a - b)) + a << endl;
  }
  return 0;
}
