#include <bits/stdc++.h>
using namespace std;
int R = pow(10, 9) + 7;
template <typename T>
void print(vector<T>& v) {
  for (int i = 0; i < v.size(); i++) {
    cout << v[i] << ' ';
  }
  cout << endl;
}
template <typename T1, typename T2>
void print(vector<pair<T1, T2>>& v) {
  cout << "[";
  for (int i = 0; i < v.size(); i++) {
    cout << '(' << v[i].first << ',' << v[i].second << "),";
  }
  cout << "]" << endl;
}
template <typename T>
void print(vector<vector<T>>& v) {
  cout << "[";
  for (int i = 0; i < v.size(); i++) {
    print(v[i]);
  }
  cout << "]" << endl;
}
template <typename T>
void print(set<T>& v) {
  cout << "{";
  for (auto i : v) {
    cout << i << ' ';
  }
  cout << "}" << endl;
}
template <typename T1, typename T2>
void print(map<T1, T2>& v) {
  cout << "{";
  for (auto i : v) {
    cout << i.first << ':' << i.second << ',';
  }
  cout << "}" << endl;
}
template <typename T>
bool in(set<T>& indices, T x) {
  return indices.find(x) != indices.end();
}
template <typename T, typename T_>
bool in(map<T, T_>& indices, T x) {
  return indices.find(x) != indices.end();
}
int power(int x, int y) {
  int res = 1;
  x = x % R;
  if (x == 0) return 0;
  while (y > 0) {
    if (y % 2 == 1) res = (res * x) % R;
    y /= 2;
    x = (x * x) % R;
  }
  return res;
}
void TestCase() {
  int n;
  cin >> n;
  string s, t;
  cin >> s >> t;
  vector<vector<int>> count1(26, vector<int>(n + 1));
  vector<vector<int>> count2(26, vector<int>(n + 1));
  for (int i = 1; i <= n; i++) {
    int index = s[i - 1] - 'a';
    for (int j = 0; j < 26; j++) {
      count1[j][i] = count1[j][i - 1];
    }
    count1[index][i]++;
  }
  for (int i = 1; i <= n; i++) {
    int index = t[i - 1] - 'a';
    for (int j = 0; j < 26; j++) {
      count2[j][i] = count2[j][i - 1];
    }
    count2[index][i]++;
  }
  vector<vector<int>> dp(n + 1, vector<int>(n + 1));
  for (int i = 0; i <= n; i++)
    for (int j = 0; j < i; j++) dp[i][j] = -1;
  for (int i = 1; i <= n; i++) {
    for (int j = i; j <= n; j++) {
      int index = s[i - 1] - 'a';
      if (count2[index][j] < count1[index][i])
        dp[i][j] = -1;
      else if (index == t[j - 1] - 'a') {
        dp[i][j] = dp[i - 1][j - 1];
      } else {
        dp[i][j] = (dp[i - 1][j] == -1) ? dp[i - 1][j] : dp[i - 1][j] + 1;
        if (dp[i][j - 1] > -1) {
          if (dp[i][j] == -1 || dp[i][j] > dp[i][j - 1]) {
            dp[i][j] = dp[i][j - 1];
          }
        }
      }
    }
  }
  cout << dp[n][n] << '\n';
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int T;
  T = 1;
  cin >> T;
  for (int tt = 1; tt <= T; tt++) {
    TestCase();
  }
}
