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 add the exponents. For this problem, you will have to use this rule twice. The correct answer is $\displaystyle{7}{{y}}^{{9}}\usepackage{cmbright}\Huge\$ .