An industrial machine costing $10,000 will produce net cash savings of $4,000 per year. The machine has a five-year useful life but must be returned to the factory for major repairs after three years of operation. These repairs cost $5,000. The company's MARR is 10% per year. Analyse the sensitivity of the IRR to +/- $2000 changes in the repair cost. What is the maximum repair cost that would still make the investment economical?

$1,000

$3,000

$5,000

$7,000

$9,000