There are several information's of immense importance already given in the question. Based on those given information's, the answer can be easily deduced.
Vertical distance between the floors = 90 feet
Angle of the escalator with the ground = 30 degrees
Let us assume the length of the escalator = x feet
Then
Sin (30) = 90/x
0.5 = 90/x
x = 90/0.5
= 180 feet
I hope the procedure is clear enough for you to understand and this is the answer that has come to your desired help.