int main()
{
	char a[10][100],b[10][100];
	int n,i,j,lengtha[10],lengthb[10],begin;
	scanf("%d",&n);
	for(i=0;i<10;i++)for(j=0;j<100;j++){a[i][j]='\0';b[i][j]='\0';}
	for(i=0;i<10;i++){lengtha[i]=0;lengthb[i]=0;}
	for(i=0;i<n;i++)
	{
		scanf("%s",a[i]);
		scanf("%s",b[i]);
	}
	for(i=0;i<n;i++)
	{
		for(j=0;a[i][j]!='\0';j++)lengtha[i]++;
        for(j=0;b[i][j]!='\0';j++)lengthb[i]++;
		for(j=lengthb[i]-1;j>=0;j--)b[i][j+lengtha[i]-lengthb[i]]=b[i][j];
		for(j=0;j<lengtha[i]-lengthb[i];j++)b[i][j]='0';
		for(j=lengtha[i]-1;j>=0;j--)
		{
			if(b[i][j]<=a[i][j]){a[i][j]=a[i][j]-b[i][j]+48;}
			else{a[i][j]=10+a[i][j]-b[i][j]+48;a[i][j-1]--;}
		}
		begin=0;
		for(j=0;j<lengtha[i]-1;j++){if(a[i][j]!='0'){printf("%c",a[i][j]);begin=1;}else if(begin==1)printf("%c",a[i][j]);}
		printf("%c",a[i][lengtha[i]-1]);
		printf("\n");
	}
	return 0;
}