/**
 * ? ? ???????
 * ?    ?????
 * ????: 2010?11?19?
 * ???????????????
*/
int main()
{
	int k, n;		//????n?????????
	cin>>n;
	for ( k =1; k <= n; k++ )	//????
	{
	int a1[201];	//????????????a1??????b1????
	int b1[201];	
	char a[201];		//?????????a??????b????
	char b[201];
	cin>>a>>b;
	int len1 = strlen(a);	//????????????
	int len2 = strlen(b);
	memset(a1,0,sizeof(a1));	//????????0
	memset(b1,0,sizeof(b1));
	int i, j = 0;
	for (i = len1 - 1; i >= 0; i--)
		a1[j++] = a[i] - '0';	//???????????????
		j = 0;
	for (i = len2 - 1; i >= 0; i--)
		b1[j++] = b[i] - '0';
	for (i = 0; i < len1 ; i++)		//????
	{
	if ( a1[i] >= b1[i] )		//????????
	{
		a1[i]= a1[i]- b1[i];
	}
	else
		if ( a1[i] < b1[i] )	//??????????????????
	{
		a1[i]= a1[i] + 10 - b1[i];
		a1[i+1]--;
	}
	}
	i = len1;
	while( a1[i] == 0 )
		i--;			//???????0??
	for(; i >= 0; i--)
	cout << a1[i];		//??????
	cout << endl;
	}
	return 0;
}
