Three-fifth of the square of a certain number is 126.15. What is the numbers ?

Answer: Option A

$$\begin{array}{rl}& \text{Let the number be }x\\ & \text{Then,}\\ & \iff \frac{3}{5}{x}^2=126.15\\ & \iff x^2=\left(126.15\times \frac{5}{3}\right)\\ & \iff x^2=210.25\\ & \iff x=\sqrt{210.25}\\ & \iff x=14.5\end{array}$$