The total sales of S (in thousands of DVD's) of a certain movie are given by the following formula where t is the number of months since the release of the DVD. Use the formula to answer the questions. S(t)= 40t2 2+150 a) Find S'(t). S'(t)= b) Find S(15) and S'(15). The value of S(15) rounded to the nearest hundredth is The value of S'(15) rounded to the nearest hundredth is What do the values for S(15) and S'(15) indicate? OA. After 15 months, the total sales are 24,000 DVD's and the sales are increasing at the rate of 1.28 DVD's per month. OB. After 15 months, the total sales are 1280 DVD's and the sales are increasing at the rate of 24 DVD's per month. OC. After 15 months, the total sales are 12,800 DVD's and the sales are increasing at the rate of 2400 DVD's per month.