Hello, can someone help me with this question, please?

Suppose that a company's daily sales volume attributed to an advertising campaign is given by the following equation. S(t) = 8/t + 6 - 64/(t+ 6)^2 + 4 (a) Find how long it will be before sales volume is maximized. t = (No Response) days (b) Find how long it will be before the rate of change of sales volume is minimized. That is, find the point of diminishing returns. t = (No Response) days