Let's say Tim invested 50% of his money to buy ABC Corp.'s shares and 50% of his money to buy DEF Corp.'s shares in 2017. From 2018 to 2021, ABC Corp. generated the total return percentage of 11%, 13%, 11%, 12%. DEF Corp. generated the total return percentage of -10%, 30%, -11%, and 29% during the same time period. What was the average rate of return for the portfolio (plain English: Tim's investment as a whole) from 2018 to 2021? NOTE: For the purpose of this question, please use the arithmetric average, not the geometric average. O 8.53% O 9.61% O 2.66% O 10.63%