import java.io.IOException;
import java.io.FileReader;
import java.io.BufferedReader;
import java.util.Scanner;

class Main 
{
	public static final boolean DEBUG = false;
	
	public static void main(String[] args) throws IOException
	{
		Scanner cin;
		String s1, s2;
		int n;
		
		if (DEBUG) {
			cin = new Scanner(new BufferedReader(new FileReader("d:\\OJ\\uva_in.txt")));
		} else {
			cin = new Scanner(System.in);
		}
		
		n = cin.nextInt();
		while (n-- > 0) {
			s1 = cin.next();
			s2 = cin.next();
			
			int a1 = Integer.parseInt(s1), a2 = Integer.parseInt(s2);
			int ans1 = a1 + a2;
			
			StringBuffer tmp1 = new StringBuffer(s1);
			StringBuffer tmp2 = new StringBuffer(s2);
			s1 = tmp1.reverse().toString();
			s2 = tmp2.reverse().toString();
			a1 = Integer.parseInt(s1);
			a2 = Integer.parseInt(s2);
			
			int ans2 = a1 + a2;
			s1 = new Integer(ans1).toString();
			tmp1 = new StringBuffer(s1);
			s1 = tmp1.reverse().toString();
			ans1 = Integer.parseInt(s1);
			if (ans1 == ans2) {
				System.out.println(tmp1.reverse().toString());
			} else {
				System.out.println("NO");
			}
		}
	}
}