We use the trigonometric function for this case. An escalator is an inclined path. We form a right triangle since we have given the value of the height. The height from the first floor to second floor is called the adjacent while the travelled distance of the people is called the hypothenuse. We use cosine function because we are given in terms of adjacent and hypothenuse. The ratio of cosine function is cos x = a/h where x is the angle Solving for h, h = a/(cos x) = 21/(cos 30) = 24.25 ft