A company has the option to buy a machine for $40000 that will never wear out or buy a machine at a cost of $4000 that will last for 3 years with no salvage value . If the company buys the $4000 machine, what minimum rate of return in % is required on the initial savings to perpetually buy another machine for $4000 every 3 years using the interest earned from the savings? (Ignore the impact of inflation and assume the machine price of $4000 remains the same in 3 years)