import java.io.*;

/**
 * Created by pdhinwa on 21/04/17.
 */
public class Main {

    void main() throws IOException {
        Reader reader = new Reader();
        Writer writer = new Writer();

        int T = reader.readInt();
        Checker.check(T, 1, 10);
        while (T-- > 0) {
            int[] a = reader.readArray();
            Checker.check(a.length == 2);
            int N = a[0];
            int K = a[1];
            Checker.check(N, 1, 100000);
            Checker.check(K, 1, (int) 1e9);
            Checker.check(N * (long) K, 1, (long) 1e9);

            String s = reader.readString();
            Checker.check(s.length() == N);
            for (int i = 0; i < N; i++) {
                Checker.check(s.charAt(i), 'a', 'z');
            }

            long res = 0;
            int cnta = 0;
            int cntb = 0;
            for (int i = 0; i < N; i++) {
                if (s.charAt(i) == 'a') {
                    cnta++;
                }
                if (s.charAt(i) == 'b') {
                    res += cnta;
                    cntb++;
                }
            }

            // (a, b) lie in the same group of strings.
            long ans = res * K;
            // (a, b) belong to different group of strings.
            ans += K * (long) (K - 1) / 2 * cnta * cntb;

            writer.println(ans);
        }

        writer.close();
        reader.readEof();
    }


    public static void main(String[] args) throws IOException {
        try {
            new Main().main();
        } catch (Exception e) {
            e.printStackTrace();
            throw e;
        }
    }

    private class Writer extends PrintWriter {
        Writer() throws FileNotFoundException {
            super(System.out);
        }

        Writer(File file) throws FileNotFoundException {
            super(file);
        }
    }

    private class Reader {
        String[] data;
        BufferedReader bufferedReader;

        Reader() {
            bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        }

        Reader(File file) throws FileNotFoundException {
            bufferedReader = new BufferedReader(new FileReader(file));
        }

        String readString() throws IOException {
            return bufferedReader.readLine();
        }

        void readEof() throws IOException {
            Checker.check(readString() == null);
        }

        int readInt() throws IOException {
            return Integer.parseInt(readString());
        }

        int[] readArray() throws IOException {
            data = readString().split(" ");
            int[] res = new int[data.length];
            for (int i = 0; i < res.length; i++) {
                res[i] = Integer.parseInt(data[i]);
            }
            return res;
        }
    }

    private static class Checker {
        private static void check(long x, long L, long R) {
            if (x < L || x > R) {
                throw new RuntimeException();
            }
        }

        private static void check(boolean b) {
            if (!b) {
                throw new RuntimeException();
            }
        }

        private static void check(int x, int L, int R) {
            if (x < L || x > R) {
                throw new RuntimeException();
            }
        }
    }
}