So the water is 36.03056/147.01396 = .245082576 but that is only accurate to three decimals (because the mass of Ca was only given to three decimals) so we write .245 and that is 24.5%
This is not my answer but I found it on Yahoo answers and it was answered by Anonymous.
Its the other way around actually. Benzoic acid is stronger than acetic acid because the electron-donating inductive effect (+I) by the alkyl group on acetic acid destabilise the conjugate base of acetic acid.