21 . Which option is correct? Show work please

Question 21 4 pts 600072 Suppose the annual sales S of a new product is given by S = 6+12 -, 0515 3 where z is time in years. Find the exact time when the annual sales are increasing at the greatest rate. Round your answer to three decimal places. Of= 2.32 years Of= 1.732 years 1= 1.989 years Of = 1.414 years Of= 1.871 years