Question

this reference photo is 5\ x 7\. as luck would have it, you want to make a 5\ x 7\ painting from this photo. so drawing the grid will be pretty straightforward. but if you want to make a large painting, you could also make a painting that is 10\ x 14\ or 15\ x 21\ or 20\ x 28\. why those sizes and not other sizes? because those sizes are the same ratio as the 5\ x 7\ reference photo. in other words, \\(\frac{5}{7} = \frac{10}{14} = \frac{15}{21} = \frac{20}{28}\\) see? its basic math. the size of your artwork must always be equally proportionate to the size of the reference photo. because of this, its important to be aware of what size canvases and wood panels are commercially available. 7. the size of the artwork must be equally proportionate to the size of the ________.

Explanation:

The text explains that artwork sizes must match the proportional ratio of the reference photo. The reference is 5" x 7", so valid scaled sizes maintain the $\frac{5}{7}$ ratio, and the blank asks what the artwork must be proportionate to, which is clearly stated in the surrounding text.

Answer:

reference photo