#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
template <typename T1, typename T2>
inline void chkmin(T1 &x, const T2 &y) {
  if (x > y) x = y;
}
template <typename T1, typename T2>
inline void chkmax(T1 &x, const T2 &y) {
  if (x < y) x = y;
}
const int INF = 1e9 + 228 + 1337;
bool check(string s, string t) {
  sort(s.begin(), s.end());
  sort(t.begin(), t.end());
  return s == t;
}
void solve() {
  int n;
  vector<string> a(2);
  cin >> n >> a[0] >> a[1];
  if (!check(a[0], a[1])) {
    cout << -1 << "\n";
    return;
  }
  vector<vector<int>> dp(n + 1, vector<int>(n + 1, INF));
  dp[0][0] = 0;
  vector<vector<vector<int>>> cnt(
      2, vector<vector<int>>(n + 1, vector<int>(26, 0)));
  reverse(a[0].begin(), a[0].end());
  reverse(a[1].begin(), a[1].end());
  for (int it = 0; it < 2; it++) {
    for (int i = 1; i <= n; i++) {
      for (int alpha = 0; alpha < 26; alpha++) {
        cnt[it][i][alpha] = cnt[it][i - 1][alpha];
      }
      cnt[it][i][a[it][i - 1] - 'a']++;
    }
  }
  for (int i = 0; i <= n; i++) {
    for (int j = 0; j <= i; j++) {
      if (i + 1 <= n && a[0][i] == a[1][j]) {
        assert(j + 1 <= n);
        chkmin(dp[i + 1][j + 1], dp[i][j]);
      }
      char x = a[1][j] - 'a';
      if (j + 1 <= n && cnt[0][i][x] > cnt[1][j][x]) {
        chkmin(dp[i][j + 1], dp[i][j]);
      }
      if (i + 1 <= n) {
        chkmin(dp[i + 1][j], dp[i][j] + 1);
      }
    }
  }
  int ans = -1;
  if (dp[n][n] != INF) {
    ans = dp[n][n];
  }
  cout << ans << "\n";
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
