A man on the top of a vertical tower observes a car moving at a uniform speed towards the tower on a horizontal road. If it takes $18 \min$ for the angle of depression of the car to change from $30°$ to $45°$, then the time taken (in $\min$) by the car to reach the foot of the tower is

• A

  $\frac{9}{2}\left(\sqrt{3}-1\right)$
• B

  $18\left(1+\sqrt{3}\right)$
• C

  $18\left(\sqrt{3}-1\right)$
• Correct answer
  D

  $9\left(1+\sqrt{3}\right)$

Hence, the correct answer is option: 'D'.