computing an internal rate of return

12-4:

DR, Whiten has decided to purchase equioment that has a cost of $60,000 and will produce a pretax net cash inflow of $30,000 per year over its estimated useful life of six years. the equipment will ahve no salvage value and will be depreciated by the staright line-method. the tax rate is 50%. determine DR. Whitten's approximate after tax internal rate of return.