Mr. Brust and Mr. Kelly have invested some of their money in the stock market, which had been fluctuating over time. The projected value of Mr. Brush’s assets after t years is t^3 + 2t^2 - 3t +400. Mr. Kelly’s projected assets after t years is t^4 - 5t^2 + 100. a) how much did each of them invest? b) what is their combined wealth after 7 years? c) what is their combined wealth after t years?