As an individual investor, you have three funds to invest into. The first is an equity fund, the second is a corporate bond fund, and the third is a T-bill money-market fund (your risk-free asset).

Fund	Expected rate of return	Risk (Standard deviation)
Equity fund	28%	40%
Corporate bond fund	13%	21%
T-bill money market fund	3%

Correlation between equity fund and bond fund returns is -0.8.

Find the risk (standard deviation) of the optimal portfolio formed from Equity and Bond funds.