#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int a, b, c;
  int t;
  cin >> t;
  while (t--) {
    cin >> a >> b >> c;
    if (c % 2 == 0)
      cout << (a - b) * (c / 2) << endl;
    else
      cout << ((a - b) * (c - 1) / 2) + a << endl;
  }
  return 0;
}
