HW Q17I need help on my homework

A company incurs debt at a rate of D'(t) = 84(t+ 6) vt" + 12t dollars per year, where t is the amount of time (in years) since the company began. By the 4th year the company had accumulated $15,286 in debt. (a) Find the total debt function. (b) How many years must pass before the total debt exceeds $40,000? (a) The total debt function is D(t) = (Use integers or fractions for any numbers in the expression.) (b) In years the total debt will exceed $40,000. (Round to three decimal places as needed.)