import java.io.*;


public class poisoned
{
	public static void main(String[] args) throws Exception
	{
		BufferedReader in=null;
		in=new BufferedReader(new FileReader("poisoned.in"));
		int numInputs=Integer.parseInt(in.readLine());
		for(int k=0;k<numInputs;k++)
		{
			int s,b;
			String[] split=in.readLine().split(" ");
			s=Integer.parseInt(split[0]);
			b=Integer.parseInt(split[1]);
			Base[] bases=new Base[b];
			for(int x=0;x<b;x++)
			{
				bases[x]=new Base(s,in.readLine());
			}
			Base target=new Base(s,in.readLine());
			//System.out.println(target);
			int bad=0;
			for(int x=0;x<b;x++)
				if((bases[x].rep | target.rep) > target.rep)
				{
					bases[x].valid=false;
					bad++;
				}
			Base[] good=new Base[b-bad];
			int index=0;
			long currID=1;
			for(int x=0;x<b;x++)
				if(bases[x].valid)
				{
					good[index++]=bases[x];
					good[index-1].id=currID;
					currID*=2;
					//System.out.println(good[index-1]);
				}
			int numTry=good.length;
			int max=(int)(Math.pow(2,numTry)+0.5);
			int min=-1;
			for(int n=0;n<max;n++)
			{
				long current=0;
				int elems=0;
				for(int x=0;x<numTry;x++)
				{
					long result=good[x].id & ((long)n);
					//System.out.println("result: "+result+" of "+good[x].id+" "+(long)n);
					if(result > 0)
					{
						//System.out.println("Trying "+good[x]);
						current=current|good[x].rep;
						elems++;
					}
				}
				if(current==target.rep && (min<0 || elems<min))
					min=elems;
			}
			System.out.println("Data Set "+(k+1)+":");
			if(min>=0)
				System.out.println(min);
			else
				System.out.println("Impossible.");
			if(k<numInputs-1)
				System.out.println();
		}
		
	}

}
class Base
{
	public int[] compound;
	public boolean valid;
	public long rep;
	public long id;
	public Base(int num,String stuff)
	{
		compound=new int[num];
		for(int x=0;x<num;x++)
			compound[x]=stuff.charAt(x)=='y'?1:0;
		compute();
		valid=true;
	}
	public Base(int num)
	{
		compound=new int[num];
		valid=true;
	}
	public boolean equals(Base other)
	{
		for(int x=0;x<compound.length;x++)
			if(compound[x]!=other.compound[x])
				return false;
		return true;
	}
	public Base and(Base other)
	{
		Base temp=new Base(compound.length);
		for(int x=0;x<compound.length;x++)
		{
			temp.compound[x]=compound[x]*other.compound[x];
		}
		temp.compute();
		return temp;
	}
	private void compute()
	{
		rep=0;
		long mult=1;
		for(int x=0;x<compound.length;x++)
		{
			rep+=compound[x]*mult;
			mult*=2;
		}
	}
	public String toString()
	{
		String s="";
		for(int x=0;x<compound.length;x++)
			if(compound[x]>0)
				s=s+"1";
			else
				s=s+"0";
		return s+" = "+rep+" id="+id;
	}
}