The perimeter of a rectangle is 35 cm. The rectangle's area (in sq. cm) as a function of its length (in cm) is graphed. What is the approximate average rate at which the area decreases, as the rectangle's length goes from 13 cm to 16 cm?

Options:
1: 10 1/3
2: 10 2/3
3: 11
4: 11 1/3