Monterey Corporation Is Considering the Purchase of a Machine Costing

Monterey Corporation is considering the purchase of a machine costing $36,000 with a six-year useful life and no salvage value.Monterey uses straight-line depreciation and assumes that the annual cash inflow from the machine will be received uniformly throughout each year.In calculating the accounting rate of return,what is Monterey's average investment?

A) $6,000
B) $7,000
C) $18,000
D) $21,000
E) $36,000