28 .to explain they want to know the missing side and the triangles are equal to each-other just one is projected smaller than the other . So the one with 16 16 and 24 is the smaller one . The difference between 24-16 is 8 . And In the bigger one the sides 20 and 20 where given so since the smaller one is equal to the bigger one you just do 20+8=28
