please help multiple choice

CMR has no debt. The stock's beta is 1.5 and its expected profitability, RE, is 15%. The company decides to go into debt at the risk-free rate, Rf, of 5% to buy back 50% of its shares. Capital markets are supposed to be perfect.

Calculate the return required by shareholders following this redemption.

a) 15%

b)20%

c)25%