Question

a 15 foot tall tree is next to a slide tree is casting a shadow of 20 feet and the slide is casting a shadow that is 16 feet how tall is the slide

Answer 1

You would first write a proportion like this:
15 over 20 = x over 16
Cross multiply 15 times 16 and 20 times x.
15 times 16 = 240. 20 times x = 20x.
Divide both sides by 20. 
240/20 = 12
x = 12
The slide tree is 12 feet tall.