The average weight of A, B and C is 45 kg. If the average weight of A and B be 40 kg and that of B and C be 43 kg, then what is the weight of B?

A+B+C=135 A+B=80 80+C=135 C=135-80 C=55 B+C=86 B+55=86 B=86-55 B=31