if 8 men each weigh 94 kg on average, then the whole team together weighs 752Kg (8 x 94).
if there are now 9 men each weighing an average of 92 Kg then the total team weighs 828Kg (9 x 92)
so to find the weight of the substitute you have to subtract the first answer from the second one, so...
828-752= 76Kg