void main()
{
	char a[30][100], b[30][100], c[30][100];
	int n, i, j, p[100], q[100], alpha[30][100], beta[30][100], gama[30][100];
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%s",a[i]);
		scanf("%s",b[i]);
		for(j=0;a[i][j]!='\0';j++);
		p[i]=j;
		for(j=0;b[i][j]!='\0';j++);
		q[i]=j;
		for(j=0;j<p[i];j++)
			alpha[i][j]=a[i][p[i]-1-j]-48;
		for(j=0;j<q[i];j++)
			beta[i][j]=b[i][q[i]-1-j]-48;
		for(j=q[i];j<p[i];j++)
			beta[i][j]=0;
		for(j=0;j<p[i];j++)
		{
			gama[i][j]=alpha[i][j]-beta[i][j];
			if(gama[i][j]<0)
			{
				gama[i][j]+=10;
				alpha[i][j+1]-=1;
			}
		}
		for(j=0;j<p[i];j++)
			c[i][j]=gama[i][p[i]-1-j]+48;
	}
	for(i=0;i<n;i++)
	{
		for(j=0;c[i][j]=='0';j++);
		for(;j<p[i];j++)
			printf("%c",c[i][j]);
		printf("\n");
	}
}