The triangles are similar because they both have the same same angles.
Why? Because the two triangles are both right triangles and they both have another angle that is the same (as indicated by the circle fragment on the picture). That means that the last angle will be the same. Triangles are similar when they have the same angles but don't have to have the same lengths.
If the triangles are similar, the side lengths are in ratios. You are given the length of the side that corresponds with the third angle, which are 4 and 15. So the ratio of the lengths of the small to large triangle is 4:15. You are given another length (Height of Annie's eyes), which is 5. This can help you find the height of the house.
Let x=height of the house.
So 4/15 = 5/x
4x=5*15=75
x=75/4
x=18.75 ft
Hope this helps!
