#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, j, k, n, t, blow, head, d, h, mx, mxd;
  cin >> t;
  while (t--) {
    cin >> blow >> head;
    mx = -1;
    mxd = 0;
    while (blow > 0) {
      cin >> d >> h;
      mx = max(mx, d - h);
      mxd = max(mxd, d);
      blow--;
    }
    if (mx <= 0 && mxd < head) {
      cout << -1 << endl;
      continue;
    }
    int val = (head - mxd) / (mx);
    if ((head - mxd) % mx != 0) val++;
    val++;
    if (mxd >= head) val = 1;
    cout << val << endl;
  }
  return 0;
}
