Question 4 Suppose that the CAPM is valid. (a) Use at most three sentences to explain why if the average investor is fully invested in the market portfolio, then the Sharpe Ratio of the market portfolio can be expressed as [E(IM) - rf] / OM= A* OM where A is the average investor's risk aversion coefficient. (b) Following Part (a), explain why during an economic boom, there can be a decline of the Sharpe Ratio. Use at most three sentences