A machine costing $1.55 million requires 4 operators at $340 per day. The machine can do the work of 50 labors at $190 per day. Fuel, oil and maintenance for the machine is $60/day. The life of the machine is six years with no salvage value. If money is worth 7%, how many days of operation per year are necessary to make purchase of the machine economical?

1. 29 days
2. 34 days
3. 40 days
4. 42 days
5. None of the above

Explanation with calculations would be appreciated. :) Thank you in advance!