#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
int w;
int dp[2005][2005];
string s, t;
int quick_s[2005][30], quick_ts[2005][30];
int solve(int i, int j) {
  if (i == 0)
    return 0;
  else {
    int cur;
    if (dp[i - 1][j] == INF)
      cur = solve(i - 1, j) + 1;
    else
      cur = dp[i - 1][j] + 1;
    if (s.at(i) == t.at(j)) {
      if (dp[i - 1][j - 1] == INF)
        dp[i][j] = solve(i - 1, j - 1);
      else
        dp[i][j] = dp[i - 1][j - 1];
      dp[i][j] = min(dp[i][j], cur);
      return dp[i][j];
    } else if (j >= i) {
      int prob = t.at(j) - 'a';
      if (quick_ts[j][prob] > quick_s[i][prob]) {
        if (dp[i][j - 1] == INF)
          dp[i][j] = solve(i, j - 1);
        else
          dp[i][j] = dp[i][j - 1];
      } else {
        if (dp[i - 1][j] == INF)
          dp[i][j] = solve(i - 1, j) + 1;
        else
          dp[i][j] = dp[i - 1][j] + 1;
      }
      dp[i][j] = min(cur, dp[i][j]);
      return dp[i][j];
    } else {
      return 0;
    }
  }
}
int main() {
  cin >> w;
  while (w--) {
    int n, i, j;
    cin >> n >> s >> t;
    for (i = 0; i <= n; i++) {
      dp[0][i] = 0;
    }
    for (i = 0; i < 30; i++) {
      quick_s[0][i] = 0;
      quick_ts[0][i] = 0;
    }
    quick_s[0][s.at(0) - 'a'] = 1;
    quick_ts[0][t.at(0) - 'a'] = 1;
    for (i = 1; i < n; i++) {
      for (j = 0; j < 30; j++) {
        if (j == s.at(i) - 'a')
          quick_s[i][j] = quick_s[i - 1][j] + 1;
        else
          quick_s[i][j] = quick_s[i - 1][j];
        if (j == t.at(i) - 'a')
          quick_ts[i][j] = quick_ts[i - 1][j] + 1;
        else
          quick_ts[i][j] = quick_ts[i - 1][j];
      }
    }
    bool pass = true;
    for (i = 0; i < 30; i++) {
      if (quick_s[n - 1][i] != quick_ts[n - 1][i]) {
        pass = false;
      }
    }
    for (i = 1; i < n; i++) {
      for (j = i; j < n; j++) {
        dp[i][j] = INF;
      }
    }
    if (pass)
      cout << solve(n - 1, n - 1) << "\n";
    else
      cout << -1 << "\n";
  }
  return 0;
}
