Answer:
The angles in a triangle should always add up to 180 degrees.
The four angles made by a set of intersecting lines will always add up to 360 degrees and the ones across from eachother are always the same.
This means that the triangle's unmarked angle is 60 degrees.
2*24 = 48 and 3*24 = 72 48 + 72 + 60 = 180 degrees
24 will be your correct answer.