Can you tel me how to calculate "Average amount invested", and please help me to solve this question, thanks.

Davio operates a chain of sub shops. The company is considering two possible expansion plans. Plan A would open eight smaller shops at a cost of $8,340,000. Expected annual net cash inflows are $1,650,000 with zero residual value at the end of ten years. Under Plan B, Davio would open three larger shops at a cost of $8,240,000. This plan is expected to generate net cash inows of $1 ,050,000 per year for ten years, the estimated life of the properties. Estimated residual value is $1,000,000. Davio uses straight-line depreciation and requires an annual return of 6%. Ncw compute the ARR (accounting rate of return) for both plans. (Round the percentages to the nearest tenth percent.) PlanA |:|% Plan B l %