Make sure to set up the proportion correctly. This is the solution to $\displaystyle\frac{{60}}{{1}}=\frac{{n}}{{720}}\usepackage{cmbright}\Huge\$ .

Each ratio should compare things in the same order, such as words to minutes. The correct proportion would have been $\displaystyle\frac{{60}}{{1}}=\frac{{720}}{{n}}\usepackage{cmbright}\Huge\$ .