You mixed up the number of T-shirts and pairs of shorts. Remember to check your answer against the original information. Eighteen T-shirts sell for $\displaystyle{18}\cdot{12}={216}\usepackage{cmbright}\Huge\$ dollars, while 21 pairs of shorts sell for $\displaystyle{21}\cdot{9}={189}\usepackage{cmbright}\Huge\$ dollars. This would be a total of $405, not $414.