I'm assuming you don't know the definition of similarity, which is fine, but I want to clarify just in case you don't:
Similarity is when two figures are the same in angles ONLY, and their sizes are proportional. Given this, PQR has a side 20" and TUV's respective side is 6". Now, there's a ratio:
20:6
Now, would you agree that it would then be logical that the perimeter would follow the same ratio? Where
60:P(TUV)?
Hope this helps some!