Answer: c. 62.5%
Step-by-step explanation:
I could not find a question with your exact figures but I found a similar one that can be used for reference.
Expected return is a weighted average of the expected returns of the constituent assets.
To bring about a return of 8%, William will have to allocate more money to the market portfolio because the risk free asset has a return of only 4%.
Assume therefore that(from the options) 62.5% went to the market portfolio and the rest went to the risk free asset.
Expected return is;
= (62.5% * 12%) + ( (1 - 62.5%) * 4%)
= 9%
The appropriate weight for the market portfolio is therefore 62.5%.