#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  int t;
  cin >> t;
  while (t--) {
    long long a, b, k;
    cin >> a >> b >> k;
    if (k % 2 == 0)
      cout << a * (k / 2) - b * (k / 2) << "\n";
    else
      cout << a * (k / 2 + 1) - b * (k / 2) << "\n";
  }
  return 0;
}
