Even though this is a multiplication problem, you do not multiply the exponents. Apply the product rule, which says $\displaystyle{{x}}^{{a}}\cdot{{x}}^{{b}}={{x}}^{{{a}+{b}}}\usepackage{cmbright}\Huge\$ . That is, to multiply factors with like bases you need to add the exponents. The correct answer is $\displaystyle{24}{{b}}^{{8}}\usepackage{cmbright}\Huge\$ .