A20-foot ladder is placed 12 feet from the wall. how high up the wall will the ladder reach?

Use the Pythagorean theorem

the hypotenuse is the ladder which is 20 ft and the base is 12 ft thus 

a^2 + b^2 = c^2 

a^2 + 144 = 400 
a^2 = 256 
a = 16 

so its 16 ft

You can use a calculater and divide the minutes by the $$, hope that you