A building can be air-conditioned by piping chilled water from a central refrigeration plant. Two proposals are being evaluated:

- Proposal 1: Uses 6 inch pipe and a pump, and a 30 horsepower motor. The installed cost of the 6 inch pipe and pump is $3200, the installed cost of the motor is $450, the salvage value of the system is $500 and the energy cost per hour of operation is $0.32.

- Proposal 2: Uses 8 inch pipe and a pump, and a 15 horsepower motor. The installed cost of the 8 inch pipe and pump is $4400, the installed cost of the motor is $350, the salvage value of the system is $600 and the energy cost per hour of operation is $0.18.

On the basis of a 10 year life, find the number of hours of operation per year for which the cost of the two systems will be equal if the interest rate is 9%