Suppose Rove Corporation's management takes actions that reduce the firm's risk, and its required return falls to 15%.

I just need help with the formula for this:

Suppose Rove Corporation's management takes actions that reduce the firm's risk, and its required return falls to 15%. What would the new equilibrium value of the stock be?

Previous Question: Rove Corporation's current dividend (D0) is $4 per share. The growth rate in dividends over the next three years is forecasted at 12%. After that, Rove's growth rate is expected to equal the industry average of 5%. If the required return is 18%, what is the current value of the stock?