You buy a share of stock, write an at-the-money 1-year call option for a premium of $10 and X=$105, and buy an at-the-money 1-year put option for a premium of $5 and X=$105. The share price may either go up to $120 or down to $95. The stock pays no dividends. Your strategy consists in constructing a risk-free portfolio. What would be your risk-free return in percentage?