Please answer both a & b with an explanation.

3) JKL Company's common stock just paid a dividend of $2.50 per share. Dividends are expected to grow at 25% for the first subsequent year, 15% for the second year and 3% per year forever after that. Your required return for this stock is 12%. a) Find the value of the stock today based on the two-stage growth model. b) Briefly discuss the shortcomings of the constant growth model