twenty times a positive integer is less than its square by 96. What is the integer ?

Answer: Option B

Let the integer be x
Them,
$$\begin{array}{rl}& \iff x^2-20x=96\\ & \iff x^2-20x-96=0\\ & \iff \left(x+4\right)\left(x-24\right)=0\\ & \iff x=24\end{array}$$