Please solve

The management of a large chain of frozen yogurt stores in New England believes that t days after the end of an advertising campaign, the volume V of sales is approximated by 60,000 + 60,000e - 0.43t At what rate (rounded to 2 decimal places) is the sales volume changing a. 6 days after the end of the advertising campaign? sales per day b. 8 days after the end of the advertising campaign? sales per day