Sales of functional food products the sales of functional

Question

Question: Sales of functional food products the sales of functional food products-those that promise benefits beyond basic nutrition-have risen sharply in recent years. The sales (in billions of dollars) of foods and beverages with herbal and other additives is approximated by the function

S(t) = 0.46t³ - 2.22t² + 6.21t + 17.25              (0 ≤ t ≤ 4)

Where t is measured in years, with t = 0 corresponding to the beginning of 1997. Show that s is increasing on the interval [0, 4].