Machine A costs $20,000, has zero salvage value at any time, and has associated labor of $1.15 for each and every piece produced on it. Machine B costs $36,000, has zero salvage value at any time, and has associated labor cost of $0.90. Neither machine can be employed except to produce the produce stated. If the interest rate is 10% and the annual rate of production is 20,000 units, how many years will it take for the cost of the two machines to break even?