If the two rectangles are similar, their sides must be proportional. We can figure this out by setting up a proportion. We need to make sure to match up the correct sides though. We know the two longer sides must match up, so 6 goes with 60, and 3 goes with 30:
3/6=30/60
If we reduce the fractions, we get:
1/2=1/2
Therefore, the rectangles are similar. One of them is just rotated.