19.635 square inches.
Assuming that the pots are arranged in a straight line, each pot would have a diameter of 5, because 5 • 3 = 15, and 15 is the length of the box. The radius of the base of one pot is therefore 2.5.
A = pi • r^2 = pi • 2.5^2 = 19.635 (approximation)
