Some help would be appreciated

A company has a badly designed product, but a huge advertising budget. The product sells well when it is first introducted. However, sales fall as people switch to a better product from a competitor. Given that the monthly sales S can be modeled by where S is in thousands of dollars and t is in months. After how many months will sales be maximized and what will the maximum in sales be? Sales will be maximized in [3 months The maximum sales will be 5| l