windsor, inc. is considering purchasing equipment costing $42000 with a 6-year useful life. the equipment will provide annual cost savings of $10216 and will be depreciated straight-line over its useful life with no salvage value. windsor requires a 10% rate of return. present value of an annuity of 1 period 8% 9% 10% 11% 12% 15% 6 4.623 4.486 4.355 4.231 4.111 3.784 what is the approximate internal rate of return for this investment? 10% 11% 9% 12%