#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimize("unroll-loops")

#include <bits/stdc++.h>
using namespace std;

#define pb push_back
#define mp make_pair
#define fi first
#define se second

void dbg_out() { cerr << endl; }
template <typename H, typename... T>
void dbg_out(H h, T... t) { cerr << ' ' << h; dbg_out(t...); }
#define dbg(...) { cerr << #__VA_ARGS__ << ':'; dbg_out(__VA_ARGS__); }

#define int long long

using ll = long long;
using pi = pair<int,int>;
using pl = pair<ll,ll>;
using vi = vector<int>;
using vl = vector<ll>;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

const int MAXN = 2e6 + 5;
const int MOD = 1e9+7; //998244353;
const int INF = 0x3f3f3f3f;
const ll INF64 = ll(4e18) + 5;

const int M = 2e6+100;

int tree[M][26];
int best[M];
int li = 1;

int custo[MAXN];

void add(string s){
	int at = 0;
	int foi = s.size();
	for(auto c : s){
		int id = c-'a';
		foi--;
		if(tree[at][id] == 0){
			tree[at][id] = li;
			best[li] = INF;
			assert(best[li] > 0);
			li++;
		}
		at = tree[at][id];
		assert(foi == 0 || custo[foi] > 0);
		best[at] = min(best[at],custo[foi]);
	}
}

void solve(){
	int n,k;
	cin >> n >> k;
	for(int i = 0; i < li; i++){
		for(int j = 0; j < 26; j++) tree[i][j] = 0;
		best[i] = INF;
	}
	li=1;
	vector<string> st(n);
	for(int i = 0; i < n; i++) cin >> st[i];
	vector<int> tam(n);
	int sum = 0;
	set<int> s;
	for(int i = 0; i < n; i++){
		tam[i] = st[i].size();
		sum += tam[i];
		s.insert(tam[i]);
	}
	sum += k;
	for(int i = 0; i <= sum; i++) custo[i] = INF;
	vector<vector<int>> g(sum+1);
	vector<int> dif(s.begin(),s.end());
	for(int i = k; i <= sum; i++){
		g[i-k].pb(i);
	}
	for(int i = 1; i < k; i++){
		for(auto e : dif){
			int go = i+e;
			g[go].pb(i);
		}
	}
	queue<int> q;
	q.push(0);
	custo[0] = 0;
	while(!q.empty()){
		int u = q.front(); q.pop();
		assert(u <= sum);
		assert(u == 0 || custo[u] > 0);
		for(auto v : g[u]) if(custo[v] == INF){
			custo[v] = custo[u]+1;
			q.push(v);
		}
	}
	for(int i = 0; i < n; i++) add(st[i]);
	
	vector<int> dp(n+1,INF);
	dp[0] = 0;
	string t;
	cin >> t;
	for(int i = 0; i < n; i++){
		if(dp[i] == INF) continue;
		int eu = 0;
		for(int j = i; j < n; j++){
			int id = t[j]-'a';
			if(tree[eu][id] == 0) break;
			dp[j+1] = min(dp[j+1],dp[i]+best[eu]);
		}
	}
	cout << (dp[n] == INF ? -1 : dp[n]) << '\n';
}

signed main(){

    ios::sync_with_stdio(false); cin.tie(NULL);
	for(int i = 0; i < MAXN; i++) custo[i] = INF;
    int t = 1;
    cin >> t;
	
    while(t--){
        solve();
    }

    return 0;
}