A stock is expected to pay a dividend of $10 in one year. Its future annual dividends are expected to grow by 20% pa. The next dividend of $10 will be in one year, and the year after that the dividend will be $12 (=10*(1+0.2)^1), and a year later $14.4 (=10*(1+0.2)^2) and so on forever. Its required total return is 50% pa. The total required return and growth rate of dividends are given as effective annual rates. Calculate the payback period of buying the stock and holding onto it forever, assuming that the dividends are received as at each time, not smoothly over each year. Note that you will have to find the price of the stock first.