If (64)2 - (36)2 = 20 × x, then x = ?

Answer: Option D

$$\begin{array}{rl}& 20\times x=\left(64+36\right)\left(64-36\right)\\ & 20\times x=100\times 28\\ & \therefore x=\frac{100\times 28}{20}\\ & =140\end{array}$$