( 15 )^2 + ( 18 )^2 - 20 = ?

Answer: Option D

$$\begin{array}{rl}& \text{Let, }\\ & {\left(15\right)}^2+{\left(18\right)}^2-20=\sqrt{x}\\ & \text{Then, }\\ & \sqrt{x}=225+324-20\\ & \iff x={\left(529\right)}^2\\ & \iff x=279841\end{array}$$