This is a factorization of the given expression, but $\displaystyle{3}{{a}}^{{3}}\usepackage{cmbright}\Huge\$ is not the GCF. You may have found that 3 is the GCF of the exponents and so used $\displaystyle{{a}}^{{3}}\usepackage{cmbright}\Huge\$ as part of your common factor. To find the GCF of two terms, be sure to factor each term and locate all of the common factors. The correct answer is $\displaystyle{3}{{a}}^{{6}}{\left({8}{{a}}^{{3}}-{5}\right)}\usepackage{cmbright}\Huge\$ .