Two rectangles are similar. if the height of the first rectangle is 3 inches, and the height of the second rectangle is 9 inches, how much longer is the second rectangle's perimeter?
3x as long
6x as long
9x as long
6 inches longer

If the rectangles are similar, then all of their linear dimensions
have the same ratio ... length, width, perimeter, diagonal, etc.,
For these two rectangles, anything in the bigger one that you can
measure with a ruler is 3 times as long as the same measurement
in the smaller one.

Their areas will have the square of that ratio.  For these two rectangles,
the area of the bigger one is (3²) = 9 times the area of the smaller one.