#include <bits/stdc++.h>
using namespace std;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using ll = long long int;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vd = vector<double>;
using vvd = vector<vd>;
using vvvd = vector<vvd>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using cdouble = complex<double>;
const double eps = 1e-7;
bool feq(double x, double y) { return abs(x - y) <= eps; }
bool inrange(ll x, ll t) { return x >= 0 && x < t; }
bool inrange(vll xs, ll t) {
  for (auto x : xs)
    if (!(x >= 0 && x < t)) return false;
  return true;
}
int ceillog2(ll x) {
  int ret = 0;
  x--;
  while (x > 0) {
    ret++;
    x >>= 1;
  }
  return ret;
}
ll rndf(double x) { return (ll)(x + (x >= 0 ? 0.5 : -0.5)); }
ll floorsqrt(ll x) {
  ll m = (ll)sqrt((double)x);
  return m + (m * m <= x ? 0 : -1);
}
ll ceilsqrt(ll x) {
  ll m = (ll)sqrt((double)x);
  return m + (x <= m * m ? 0 : 1);
}
ll rnddiv(ll a, ll b) { return (a / b + (a % b * 2 >= b ? 1 : 0)); }
ll ceildiv(ll a, ll b) { return (a / b + (a % b == 0 ? 0 : 1)); }
ll gcd(ll m, ll n) {
  if (n == 0)
    return m;
  else
    return gcd(n, m % n);
}
ll lcm(ll m, ll n) { return m * n / gcd(m, n); }
int main() {
  int t;
  cin >> t;
  for (int _ = 0; _ < int(t); _++) {
    int n;
    ll x;
    cin >> n >> x;
    ll f = LLONG_MIN, g = LLONG_MIN;
    for (int i = 0; i < int(n); i++) {
      ll d, h;
      cin >> d >> h;
      f = max(f, d - h);
      g = max(g, d);
    }
    if (f <= 0 && g < x) {
      cout << -1 << endl;
    } else if (x <= g) {
      cout << 1 << endl;
    } else {
      ll k = ceildiv(x - g, f);
      cout << k + 1 << endl;
    }
  }
}
