(4a) Two investments, A and B, were mixed half and half in a portfolio. The expected return for A is 15% and for B 12%. The associated variances of the rate of return are 13 and 12 respectively for A and B whilst the covariance between the two assets is 3. Find the expected return and risk of this portfolio.

(4b) If we change the proportion of A and B invested in the portfolio from 50-50, to (i) 20-80 and (ii) 70-30 whilst holding everything else the same, find the expected return and risk of the respective portfolios.