/*???1000012904
  ?????????
  ?????
  ???2010?11?19?
*/
int main()
{
	int n;
	cin >> n;//???????
	for(int i = 0; i < n; i++)
	{
		int numa[101], numb[101];//???????numa?????numb
		char stra[101], strb[101];//?????????stra,strb
		int lena, lenb;//???????lena,????lenb
		cin >> stra;
		cin >> strb;
		lena = strlen(stra);
		lenb = strlen(strb);//??????????????
		memset(numa, 0, sizeof(numa));
		memset(numb, 0, sizeof(numb));//?????
		int j = 0, k = 0;
		for(k = lena - 1; k >= 0; k--)
		{
			numa[j++] = stra[k] - '0';
		}//???????????????????numa
		j = 0;
		for(k = lenb - 1; k >= 0; k--)
		{
			numb[j++] = strb[k] - '0';
		}//??????????????????numb
		for(k = 0; k < lena; k++)
		{
			if(numa[k] < numb[k])
			{
				numa[k] = numa[k] + 10;
				numa[k + 1] = numa[k + 1] - 1;
			}//?????????????????????1????10?????1
			numb[k] = numa[k] - numb[k];//????????????????????
		}
		k = lena;
		while(numb[k] == 0)
			k--;
		//???????????????
		for( ;k >= 0; k--)
			cout << numb[k];
		cout << endl;
		cin.get();//???????????
	}
	return 0;
}

