//**************************
//*   ?????????   *
//*   ?  ?????       *
//*   ?  ??1000012738   *
//*   ?  ??2010.11.20   *
//**************************

int main()
{
	char a[101], b[101];                  //?????????????
	int c, d, n, i, j, k;                 //??????
	cin >> n;                             //??????
	for(i = 0; i < n; i ++)
	{
		cin >> a >> b;                    //?????
		c = strlen(a);                    //????
		d = strlen(b);
		int numa[100] = {0};              //????????????
		int numb[100] = {0};
		k = 0;                            //?????
		for(j = c - 1; j >=0; j --)       //??????
		{
			numa[k ++] = a[j] - '0';
		}
		k = 0;
		for(j = d - 1; j >= 0; j --)
		{
			numb[k ++] = b[j] - '0';
		}
		for(j = 0; j <= d; j ++)          //???????
		{
			numa[j] -= numb[j];
			if(numa[j] < 0)               //????????
			{
				numa[j] += 10;            //????
				numa[j + 1] --;
			}
		}
		j = c;
		while(numa[j] == 0)               //?????????0??
			j --;
		for( ; j >= 0; j --)              //??
			cout << numa[j];
		cout << endl;                     //??
	}
	return 0;
}

