4. In an index, asset A has the price of $10, with the no. of shares 500 , asset B has the price of $15, with the no. of shares 1000 , asset C has the price of $25, with the no. of shares 5000 , asset D has the price of $5, with the no. of shares 100 . Now, the prices for these four assets has changed to $8,$18, $30, \$7. Calculate the price weighted and value-weighted index return over the period. Please address the advantage and disadvantage for these two index calculation. (Please refer to the self-studying slides "Index calculation" in Lecture 1)