Answer:
the size of the painting is 39 inches by 51 inches.
Explanation:
Size of the painting: A * B
Scale factor: 1/3
Size of the photo: [1/3]A * [1/3]B
[1/3]A = 13inches => A = 13inches * 3 = 39 inches
[1/3]B = 17 inches => B = 17 inces * 3 = 51 inches.