Based on residual income, the operating income, and the minimum rate of return, the average invested assets must be $252,000.
First find the required return on assets amount as:
= Operating income - Residual income
= 31,000 - 10,840
= $20,160
This amount is equal to the 8% required rate of assets so the average invested assets is:
= Required return amount / Required return rate
= 20,160 / 8%
= $252,000
Find out more on the uses of required rate of return at https://brainly.com/question/14053729.