Well in case someone else asks.
4x5 is 20 (area of painting)
5x6 is 30 (area of painting and frame since frame adds 6inches to each side essentially adding 1ft to L and 1 ft to W)
subtract 20 from 30 for 10 as the total area sq ft of the frame
10/30=¹/3=.333 or 33%
the part that throws you off is the 'width' of the frame.