Warf Co. just paid a divident of $4 per share. The company will increase its dividend by 20% next year and then reduce its dividend growth rate by 5 percentage points each year until it reaches the industry average of 5% (i.e. 20%, 15%, 10%, and then 5%), after which the company will keep a constant growth rate, forever. If the required return on the Warf stock is 13%, what will a share of stock sell for today? How about the end of the fifth year?

I know the answer is (P3=79.695, P0=68.01159, P5=87.86) but I need someone to explain this to me in detail.