Edmund Janus
Edmund Janus voted up Tom Jackson's answer

If the two rectangles are similar, then the ratio of the side of the 3 inch to the width of the 3 inch must equal the ratio of the side of the 9 inch to the width of the 9 inch

To state that mathematically 3/x = 9/y from which y = 3x for this "family" … Read more

Edmund Janus
Edmund Janus voted up John McCann's answer

Area = width * height


Let us say the similarity is in the width. Call it 5 inches

A = 5 in * 3 in

= 15 in^2

======

A = 5 in * 9 in

= 45 in^2

======As you should have guessed the area of the second rectangle is 3 times as large as the first rectangle.