In similar figures, the angle measures are the same but the side lengths are different. So in #4, x = 42. Since all the angles of a quadrilateral added up equal 360, then y is 360-90-90-42=138. For number 5, make sure you match up the sides correctly in your ratio:
. You could cross multiply to get 4x=16, and x = 4, or you could just realize that reducing 4/8 will give you 2/4 and x = 4. Going back to the idea that in similar shapes corresponding angles are the same measure, x in #6 is 63