Correct. Create the following system:

$\displaystyle{e}={6}{n}\usepackage{cmbright}\Huge\$

$\displaystyle{232.50}-{e}={7.50}\cdot{\left({36}-{n}\right)}\usepackage{cmbright}\Huge\$

and then solve it for n, which is 25. That means $\displaystyle{36}-{n}={36}-{25}\usepackage{cmbright}\Huge\$ , which is 11.