A photo of a painting measures 13" x 17" the scale factor is 1/3 what size is the painting

Given that the paint has a dimension of 13" by 17", it implies that:

width=13" and length=17"

The scale factor of the painting is 1/3. Thus the original size was as follows'

Width=13 / (1/3) = 39"

Length=17 / (1/3) = 51'

the answer is 39" by 51"