Question 28
An escalator (moving staircase) of $n$ uniform steps visible at all times descends at constant speed. Two boys, $A$ and $Z,$ walk down the escalator steadily as it moves, $A$ negotiating twice as many escalator steps per minute as $Z.$ $A$ reaches the bottom after taking $27$ steps while $Z$ reaches the bottom after taking $18$ steps. Then $n$ is: