a=int(input()) b=[] for i in range(a): c,d=map(int,input().split()) e=c+d f=0 g=0 h=0 c=str(c) d=str(d) e=str(e) for j in range(len(c)-1,-1,-1): f=f*10+int(c[j]) for j in range(len(d)-1,-1,-1): g=g*10+int(d[j]) for j in range(len(e)-1,-1,-1): h=h*10+int(e[j]) if f+g==h: b.append(e) else: b.append("NO") for i in b: print(i)