Following is a list of various costs incurred in producing toy robotic helicopters. With respect to the production and sale of these toy helicopters, classify each cost as either variable, fixed, or mixed.
1. Oil used in manufacturing equipment
2. Hourly wages of inspectors
3. Electricity costs, $0.20 per kilowatt-hour
4. Property insurance premiums, $1,500 per month plus $0.006 for each dollar of property over $2,000,000
5. Janitorial costs $4,000 per month
6. Pension cost, $0.08 per employee hour on the job
7. Computer chip (purchased from a vendor)
8. Hourly wages of machine operators
9. Straight-line depreciation
on the production equipment
12. Rent on warehouse, $10,000 per month plus $10 per square foot of storage used
14. Property taxes, $100,000 per year on factory building and equipment
15. Salary of plant manager.