#include<bits/stdc++.h>

using namespace std;

typedef long long ll;
int const maxn = 1e6 + 5, maxc = 26;
string s[maxn];
int a[maxn];
ll imin[maxn], inf = 1e18 + 7;
long double dp[maxn];
long double f[maxn], best[maxn];
int nxt[maxn][maxc], cur = 1;

ll func(double x) {
    return x + 0.5;
}

void add(string s, int k) {
    int node = 0, n = s.size();
    for (int i = 0; i < n; i++) {
        int c = s[i] - 'a';
        if (nxt[node][c] == 0) {
            nxt[node][c] = cur++;
            best[cur - 1] = inf;
        }
        node = nxt[node][c];
        best[node] = min(best[node], n / (double)k + dp[(n - i - 1) % k]);
    }
}

main() {
#ifdef HOME
    freopen("input.txt", "r", stdin);
#endif // HOME
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t;
    cin >> t;
    while (t--) {
        int n, k, N = 0;
        cin >> n >> k;
        for (int i = 0; i < k; i++) imin[i] = inf;
        for (int i = 0; i < n; i++) {
            cin >> s[i];
            a[i] = s[i].size();
            N = max(N, a[i]);
            int w = a[i] % k;
            imin[w] = min(imin[w], (ll)a[i]);
        }
        for (int i = 0; i < k; i++) dp[i] = inf;
        dp[0] = 0;
        for (int j = 1; j < k; j++) {
            if (imin[j] == inf) continue;
            int find = 1;
            while (find) {
                find = 0;
                for (int w = 0; w < k; w++) {
                    int lst = w - j;
                    if (lst < 0) lst += k;
                    long double add = 1 + imin[j] / (double)k;
                    if (dp[lst] + add < dp[w]) {
                        dp[w] = dp[lst] + add;
                        find = 1;
                    }
                }
            }
        }
        string t;
        cin >> t;
        int m = t.size();
        t = "#" + t;
        for (int i = 1; i <= m; i++) f[i] = inf;
        for (int i = 0; i < n; i++) add(s[i], k);
        f[0] = 0;
        for (int i = 0; i < m; i++) {
            if (f[i] == inf) continue;
            int node = 0;
            for (int j = i + 1; j <= m; j++) {
                int c = t[j] - 'a';
                if (nxt[node][c] == 0) break;
                node = nxt[node][c];
                f[j] = min(f[j], f[i] + best[node] + 1);
            }
        }
        if (f[m] == inf) cout << -1 << '\n';
        else cout << func(f[m] - m / (double)k) << '\n';
        for (int i = 0; i <= cur; i++) {
            for (int j = 0; j < 26; j++) nxt[i][j] = 0;
        }
    }
    return 0;
}