#include <bits/stdc++.h>
using namespace std;
template <class T>
using vc = vector<T>;
template <class T>
using vvc = vc<vc<T>>;
template <class T>
void mkuni(vector<T>& v) {
  sort(v.begin(), v.end());
  v.erase(unique(v.begin(), v.end()), v.end());
}
long long rand_int(long long l, long long r) {
  static mt19937_64 gen(chrono::steady_clock::now().time_since_epoch().count());
  return uniform_int_distribution<long long>(l, r)(gen);
}
template <class T>
void print(T x, int suc = 1) {
  cout << x;
  if (suc == 1)
    cout << '\n';
  else
    cout << ' ';
}
template <class T>
void print(const vector<T>& v, int suc = 1) {
  for (int i = 0; i < v.size(); i++)
    print(v[i], i == (int)(v.size()) - 1 ? suc : 2);
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int T;
  cin >> T;
  while (T--) {
    int n;
    cin >> n;
    string s, t;
    cin >> s >> t;
    vc<vector<int>> ps(n + 1, vector<int>(26)), pt(n + 1, vector<int>(26));
    vc<vector<int>> dp(n + 1, vector<int>(n + 1, 1e9));
    for (int i = 1; i <= n; i++) {
      for (int j = 0; j < 26; j++) {
        ps[i][j] = ps[i - 1][j];
        pt[i][j] = pt[i - 1][j];
      }
      ps[i][s[i - 1] - 'a']++;
      pt[i][t[i - 1] - 'a']++;
    }
    bool suc = 1;
    for (int j = 0; j < 26; j++) {
      if (ps[n][j] != pt[n][j]) suc = 0;
    }
    if (!suc)
      print(-1);
    else {
      dp[0][0] = 0;
      for (int i = 0; i <= n; i++) {
        for (int j = i; j <= n; j++) {
          if (j) dp[i][j] = min(dp[i][j], dp[i][j - 1] + 1);
          if (i && s[i - 1] == t[j - 1])
            dp[i][j] = min(dp[i][j], dp[i - 1][j - 1]);
          if (i && ps[i][s[i - 1] - 'a'] <= pt[j][s[i - 1] - 'a'])
            dp[i][j] = min(dp[i][j], dp[i - 1][j]);
        }
      }
      print(dp[n][n]);
    }
  }
}
