Answer:
10 feet
Step-by-step explanation:
This is a problem of scale 
where scale is 
actual height of any object/ height of that object on drawing
given
actual height = 24 feet
this is represented 1/2 inch on drawing
thus
scale = actual height/ height on drawing = 24 feet/1/2 inch = 24*2 feet/ 1 inch 
scale = 48 feet / 1 inch 
given actual  height of a building = 480 feet
let the height on drawing be x inch
thus 
 48 feet / 1 inch = 480 feet/ x inch
=> x inch/ 1 inch = 480 feet / 48 feet
=> x = 10 feet
Thus,  the  height of  building on the drawing is 10 feet