$\displaystyle{2}\cdot{{5}}^{{2}}\cdot{7}={2}\cdot{5}\cdot{5}\cdot{7}={350}\usepackage{cmbright}\Huge\$ , not the 140 it should multiply out to. The prime factorization is $\displaystyle{2}\cdot{2}\cdot{5}\cdot{7}\usepackage{cmbright}\Huge\$ , which can be rewritten with exponents as shown in the correct answer, $\displaystyle{{2}}^{{2}}\cdot{5}\cdot{7}\usepackage{cmbright}\Huge\$ .