Lonely Guy Repair Service recently performed repair services for a customer that totaled $400. Somehow the bill was lost and the company accountant was trying to recreate the bill from memory. This is what was remembered:
| Total bill |
$600 |
| Labor profit margin |
$10 |
| Materials profit margin |
20% |
| Total labor charges |
$390 |
| Cost of materials used |
$120 |
| Total hourly cost |
$22.50 |
How many hours were billed on the job?