n=int(input()) l=[] for i in range (n): a,b = map(int,input().split()) arr=[] arr.append(str(a)) arr.append(str(b)) l.append(arr) for i in range (n): k=str(int(l[i][0])+int(l[i][1])) t="" for j in range (len(l[i][0]),0,-1): t=t+l[i][0][j-1] m="" for j in range (len(l[i][1]),0,-1): m=m+l[i][1][j-1] k1=int(t)+int(m) k2="" for j in range (len(k),0,-1): k2=k2+k[j-1] if k1==int(k2): print(k) else: print("NO")