#include <bits/stdc++.h>
const int INF = 1e9 + 7;
int ds[100];
int hs[100];
int solve() {
  int N, X;
  scanf("%d %d", &N, &X);
  for (int i = 0; i < N; i++) {
    scanf("%d %d", &ds[i], &hs[i]);
  }
  int last = *std::max_element(ds, ds + N);
  if (last >= X) return 1;
  int dec = 0;
  for (int i = 0; i < N; i++) {
    dec = std::max(dec, ds[i] - hs[i]);
  }
  if (dec == 0) return -1;
  return (X - last + dec - 1) / dec + 1;
}
int main() {
  int T;
  scanf("%d", &T);
  while (T--) {
    printf("%d\n", solve());
  }
}
