You may have correctly started with $\displaystyle{1.57}={2}{\left({3.14}\right)}\sqrt{{\frac{{L}}{{32}}}}\usepackage{cmbright}\Huge\$ and simplified to $\displaystyle{0.25}=\sqrt{{\frac{{L}}{{32}}}}\usepackage{cmbright}\Huge\$ , but when you squared the right side, you forgot to square the left side. When solving any equation, make sure that you perform the same operation on both sides.