You may have done your calculations without squaring the radius. When you substitute into $\displaystyle{V}={k}{{r}}^{{2}}{h}\usepackage{cmbright}\Huge\$ , you should first get $\displaystyle{251.2}={k}{\left({{4}}^{{2}}\right)}{\left({5}\right)}\usepackage{cmbright}\Huge\$ . Then you find k. When you are finding the volume of B, make sure that you square the radius r, which is 3.