Suppose portfolio ABC has a standard deviation of 18% and an expected return of 12. The risk-free rate is 3%. Consider an investor wishing to use ABC and the risk-free asset to achieve an expected return of 8%. What will be the overall standard deviation this investor faces? Express your answer in decimal format, rounded accurately to 4 decimal places (e.g., 10.67% should be expressed as 0.1067 and nothing else)