A20 foot ladder is leaning against the side of a building. the bottom of the ladder is 4 feet from the wall. how many feet above the ground does the ladder touch the wall?

It form a right triangle
legnth of ladder is hypotonuse
bottom of ladder from wall distance is one leg
distance up wall is other leg
a^2+b^2=c^2
c=hypotonuse and a and b are legs

4^2+b^2=20^2
16+b^2=400
minus 16 both sides
b^2=384
sqrt both sides
b=8√6 ft
aprox
b=19.59ft from ground

Hope i can you!