#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int f = 1, ans = 0;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    ans = ans * 10 + c - '0';
    c = getchar();
  }
  return f * ans;
}
const int MAXN = 2011;
int f[MAXN][MAXN], Num[2][MAXN][27], N, cas;
char S[MAXN], T[MAXN];
bool Get(int x, int y) {
  for (int i = 0; i < 26; i++)
    if (Num[0][x][i] < Num[1][y][i]) return 0;
  return 1;
}
int main() {
  cas = read();
  while (cas--) {
    N = read();
    scanf("%s%s", S + 1, T + 1);
    for (int i = 0; i <= N + 1; i++)
      for (int j = 0; j <= N + 1; j++) f[i][j] = INT_MIN;
    for (int i = 0; i <= N + 1; i++)
      for (int j = 0; j < 26; j++) Num[0][i][j] = Num[1][i][j] = 0;
    for (int i = N; i >= 1; i--) {
      for (int j = 0; j < 26; j++) Num[0][i][j] = Num[0][i + 1][j];
      Num[0][i][S[i] - 'a']++;
      for (int j = 0; j < 26; j++) Num[1][i][j] = Num[1][i + 1][j];
      Num[1][i][T[i] - 'a']++;
    }
    bool ff = 1;
    for (int i = 0; i < 26; i++) ff &= (Num[0][1][i] == Num[1][1][i]);
    if (!ff) {
      printf("-1\n");
      continue;
    }
    f[0][0] = 0;
    for (int i = 0; i <= N; i++) f[0][i] = f[i][0] = 0;
    for (int i = 1; i <= N; i++) {
      for (int j = 1; j <= N; j++) {
        f[i][j] = max(f[i - 1][j], f[i][j - 1]);
        if (Get(i, j) && S[i] == T[j])
          f[i][j] = max(f[i][j], f[i - 1][j - 1] + 1);
      }
    }
    printf("%d\n", N - f[N][N]);
  }
  return 0;
}
