network theorem

In the circuit shown in the figure the power consumed in the resistance R is measured when one source is acting at a time, these values are 18W, 50W and 50W.when all the sources are acting simultaneously the maximum possible power in R is 450W ie. [ 450 = {(18)^(1/2) + (50)^(1/2) + (98)^(1/2)}^2 ];
why not 18 + 50 + 98 = 166W.explain????????????
also explain which theorem is applicable here.