Franklin Rentals can purchase a van that costs $108.000; it has an expected useful life of four years and no salvage value. Franklin uses straight-line depreciation. Expected revenue is $45.360 per year. Assume that depreciation is the only expense associated with this investment. Requlred a. Determine the payback period. (Round your answer to 1 declmal place.) b. Determine the unadjusted rate of return based on the average cost of the investment. (Round your answer to 1 declmal place. (l.e., .234 should be entered as 23.4).)