99 × 21 - 3 ? = 1968

Answer: Option A

$$\begin{array}{rl}& \text{Let,}\\ & 99\times 21-\text{root}3\text{of}x=1968\\ & \text{Then,}\\ & \iff 2079-\text{root}3\text{of}x=1968\\ & \iff \text{root}3\text{of}x=2079-1968\\ & \iff \text{root}3\text{of}x=111\\ & \iff x={\left(111\right)}^3\\ & \iff x=1367631\end{array}$$