Varies directly as the square of the diameter square means to multiply by itself or x^2 that means k=x/y in this case x=15 y=10^2 k=15/10^2=15/100=3/20 so the new pizza is k=x/16^2 k=3/20 3/20=x/16^2 evaluate 16^2 3/20=x/256 multiply both sides by 256 768/20=x 384/10=x 38.4=x she should put about 38 slises