A plumber charges a flat fee of $50 plus $30 per hour for labor. If a customer's total bill was $170, how many hours did the plumber work?

✓ Correct Answer: Option B

Set up the equation: 50 + 30h = 170. Subtract 50 from both sides: 30h = 120. Divide by 30: h = 4. The plumber worked 4 hours.