#include<bits/stdc++.h>
using namespace std;
#define Re register int

const int N = 5005, Inf = 1000000;
int T, n, m, ans, cnt[5], ct[5], ch[200], a[N], d[5][N], f[N][N], g[N][N];
char sn[N], sm[N];

int main()
{
	scanf("%d", &T);
	ch['W'] = 0, ch['Q'] = 1, ch['B'] = 2, ch['G'] = 3;
	while (T--)
	{
		scanf("%d%d", &n, &m);
		scanf("%s", sn + 1);
		scanf("%s", sm + 1);
		cnt[1] = cnt[2] = 0;
		for (Re i = 1; i <= n; ++i) a[i] = ch[sn[i]];
		for (Re i = 1; i <= m; ++i) a[n + i] = ch[sm[i]];
		for (Re i = 1; i <= n + m; ++i)
			if (a[i] == 1) d[1][++cnt[1]] = i;
			else if (a[i] == 2) d[2][++cnt[2]] = i;
		//for (Re i = 1; i <= cnt[2]; ++i) printf("d[2][%d] = %d\n", i, d[2][i]);
		//printf("!!%d %d\n", cnt[1], cnt[2]);
		for (Re i = 0; i <= cnt[1]; ++i)
			for (Re j = 0; j <= cnt[2]; ++j)
			{
				f[i][j] = n;
				if (i) f[i][j] = max(f[i][j], f[i - 1][j] + ((f[i - 1][j] >= d[1][i]) ? 1 : 0));
				if (j) f[i][j] = max(f[i][j], f[i][j - 1] + ((f[i][j - 1] >= d[2][j]) ? 2 : 0));
				//printf("+%d %d %d\n", i, j, f[i][j]);
			}
		if (f[cnt[1]][cnt[2]] < n + m)
		{
			puts("IMPOSSIBLE");
			continue;
		}
		ct[1] = cnt[1], ct[2] = cnt[2], ans = n + m;
		for (Re i = 0; i <= cnt[2]; ++i) g[n + m + 1][i] = g[n + m + 2][i] = 0;
		for (Re i = n + m; i > n; --i)
		{
			if (a[i] == 1) --ct[1];
			else if (a[i] == 2) --ct[2];
			for (Re j = 0; j <= ct[2]; ++j)
			{
				g[i][j] = Inf;
				if (j) g[i][j] = g[i + 2][j - 1 + (a[i] == 2)];
				g[i][j] = min(g[i][j], max(1, g[i + 1][j + (a[i] == 2)] + (a[i] != 1)));
				if (g[i][j] > ct[1]) continue;
				int u = i - 1 - n - 2 * (ct[2] - j);
				if (u < 0 || u > ct[1] || ct[1] - u < g[i][j]) continue;
				int v = n + ct[2] - j;
				if (v >= ans) continue;
				if (f[u][ct[2] - j] == i - 1) ans = v;
			}
		}
		printf("%d\n", ans);
	}
	return 0;
}