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:
<spanclass=′latex−bold′>(A)</span>63<spanclass=′latex−bold′>(B)</span>54<spanclass=′latex−bold′>(C)</span>45<spanclass=′latex−bold′>(D)</span>36<spanclass=′latex−bold′>(E)</span>30