What proportion of his total investment should he invest in the risky fund in order to achieve the expected return?

What is the standard deviation of the complete portfolio?

An investor wants to invest money in Treasury bills and a risky fund managed by Infinity Capital. The investor wants to achieve an expected return of 7% on his complete portfolio. Infinity Capital has an expected return of 15% and a standard deviation of returns of 21%. T-bills have a return of 5%