You may have missed the word quarterly and used $\displaystyle{m}={1}\usepackage{cmbright}\Huge\$ . You should be using $\displaystyle{m}={4}\usepackage{cmbright}\Huge\$ , along with $\displaystyle{P}={5},{000}\usepackage{cmbright}\Huge\$ , $\displaystyle{r}={0.02}\usepackage{cmbright}\Huge\$ , and $\displaystyle{t}={10}\usepackage{cmbright}\Huge\$ . Substitute into the formula and simplify.