Michael trades T-bills with the annual rate of return equal to 2% and TD stock. The expected rate of return and standard deviation of the rate of return of TD stock are equal to 12% and 25%, respectively . The coefficient of risk aversion of Michael is 2. What is a standard deviation of his optimal portfolio?

a.

20%

b.

15%

c.

10%

d.

25%

e.

40%