A company wants to manufacture soup cans of a fixed volume. After analyzing construction costs, the company has determined that the cost of construction of the can, in cents, is given by

C(r) = 80 r + 0.3r2

where r is the radius of the can, in cm. Given that the company wants to manufacture only cans whose radii are between 3 and 8 cm, find the absolute minimum cost of construction of a can. Also find the radius of the can that the company should use to achieve the minimum cost.