It would be best if you sketch the statement in the problem. You will see that a right triangle would be made where the hypotenuse would be the length of the escalator. The horizontal distance would be the base and the vertical distance would be the height. We can use trigonometric functions to solve the base.
angle = 25 degrees
height = 42 ft
tan (25) = height / base = 42 / base
base = 90.07 ft