It should be about 16.67% (or 17%) of it.
You would multiply by 1.2 for example if you wanted to find 120% of 100 you would multiply by 1.2 and get 120
C is the correct shape.
Explanation:
The ratio of the sides must be the same for the postcard and the painting. The painting has a ratio of 30.25 to 25.25. If you simplify this and divide both sides by 5, you get 6.05 to 5.05, which matches C.
Hope that helps!
-Grace