A firm requires power shovels for its open-pit mining operation. This mining equipment, with a first cost of $500,000, has an estimated salvage value of $70,000 at the end of 10 years' service. If the firm uses a rate of interest of 15% for the project evaluation, how much must be earned on an equivalent annual basis so that the firm recovers its invested capital plus earns a return on the capital committed to the equipment during its lifetime?