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