A 25 ft ladder is placed 7 feet from the wall. How high up the wall will the ladder reach?A.18ftB.20ftC.22ftD.24ft

You set this up using Pythagorean theorem (A^2 + B^2 = C^2)
When setting up the right triangle, the problem says the ladder is placed 7 feet away, which would be the bottom of the triangle, and would be your A or B value, the ladder is leaning and is a total of 25 feet, meaning 25 is your hypotenuse and is your c value.
Then you're at A^2 +7^2 = 25^2
Square all of the integers, giving you A^2 +49 =625, then subtract 49 from each side leaving you with A^2 = 576, square root each side (√A^2 = √576)
Which will leave you at A = 24.