A 90-foot rope from the top of a tree house to the ground forms a 45∘45∘ angle of elevation from the ground. How high is the top of

You have a 45-45-90 right triangle whose hypotenuse is 90.

To find either of the sides of this triangle, divide the hypotenuse by sqrt(2).

So, your answer is  90 / sqrt(2).

Now, use your calculator to get a decimal answer ...