This is a factorization of the given expression, but $\displaystyle{{a}}^{{6}}\usepackage{cmbright}\Huge\$ is not the GCF. The GCF will contain all the variables the two terms have in common, and all the primes that the two terms have in common. The correct answer is $\displaystyle{3}{{a}}^{{6}}{\left({8}{{a}}^{{3}}-{5}\right)}\usepackage{cmbright}\Huge\$ .