//****************************************************** 
//* ? ? ?   ?? ? ? ? ?                        *
//* ? ?      ?? ? ?                              *
//* ? ? ? ??2010 ? 11 ? 17 ?                   * 
//* ? ?      ?1000010185                            *
//****************************************************** 
int main()
{
	char aa[100], bb[100]; //?????????
	int a[100], b[100], c[100];
	int n, la, lb;
	cin >> n;
	for (int i = 0; i < n; i ++)
	{
		cin >> aa >> bb;
		la = strlen(aa);
		lb = strlen(bb);
		for (int j = 0; j < la; j ++) //???????????
		{
			a[j] = aa[j] - 48;
			b[j] = bb[j] - 48;
		}
		for (int j = 1; j <= lb; j ++) //????????????
			c[la - j] = a[la - j] - b[lb - j];
		for (int j = 0; j < la - lb; j ++) //b?????????0??????
			c[j] = a[j];
		for (int j = la - 1; j > 0; j --) //??????0??????10??????1(????
			if (c[j] < 0)
			{
				c[j] += 10;
				c[j - 1] -= 1;
			}
		int k;
		for (int j = 0; j < la; j ++) //???????0??
			if (c[j] != 0)
			{
				k = j;
				break;
			}
		for (int j = k; j < la; j ++) //????
			cout << c[j];
		cout << endl;
	}
	return 0;
}