What is the angle of the question mark?

Why are you confused? EP said that the angle at the vertex that they(the equilateral triangle and the square share)  is a right angle, or 90 degrees . Then the middle angle of the equilateral triangle is 60 degrees. Why? Because "equilateral" triangle has 3 "equal" sides and, therefore, 3 "equal" angles!!. Since the sum of the 3 angles of ANY triangle is 180 degrees, then 180/3 =60 degrees for each angle. Since the angle at the vertex is "splitting" a right angle, or 90 degrees which belongs to the square, then that leaves 2 smaller angles on each side of the 60-degree angle, or 90 - 60 =30/2 =15 degrees. That is the top angle of the triangle you are trying to solve.

Since that small triangle is a RIGHT triangle, then: 180 - 90 - 15 =75, which is the angle with a question mark?

because they could drop even lower..

pay attention in your classes and concentrate the best thing you can do to raise your test scores is to pay attention when you're supposed to be learning the material: in class!

take good notes.

do your homework.

use mnemonics and other tricks.

do practice tests.

note: the best i know.