int main()
{
	char str1[251], str2[251];
	int i = 0, j = 0, len1, len2, a[251], b[251], pos = 0, n, k;
	cin >> n;
//    memset(c,0,sizeof(c));
	for(k = 1;k <= n;k++)
	{
		cin >> str1 >> str2;
		len1 = strlen(str1);
		len2 = strlen(str2);
	    memset(a,0,sizeof(a));
		memset(b,0,sizeof(b));
		j = 0;
		for(i = len1 - 1;i >= 0;i--)
			a[j++] = str1[i] - '0';
		j = 0;
		for(i = len2 - 1;i >= 0;i--)
			b[j++] = str2[i] - '0';
		for(i = 0;i < len1;i++)
		{
			a[i] = a[i] - b[i];
			if(a[i] < 0)
			{
				a[i] = a[i] + 10;
				a[i+1] = a[i+1] - 1;
			}
		}
		for(i = len1 - 1; i >= 0;i--)
			if(a[i] != 0)
			{
				pos = i;
				break;
			}
		for(i = pos;i >= 0;i--)
			cout << a[i];
		cout << endl;
	}
	return 0;
}
