Gallons of fuel remaining for 30 minutes at the same burn rate?

• A. 6
• B. 9
• C. 8
• D. 10

Answer: (B)

Constant burn rate means fuel is used at a fixed amount each minute, so the fuel remaining changes linearly with time. The amount consumed in 30 minutes is 30 times the per-minute burn rate, and you subtract that from the starting fuel to get what’s left: remaining = starting_fuel − 30 × burn_rate.

In this problem, applying that relationship with the given starting amount and burn rate leaves 9 gallons after 30 minutes. So the remaining fuel is 9 gallons, which is why that option is chosen. If you tried 6, 8, or 10, you’d be implying a different starting amount or burn rate that doesn’t fit the 30-minute period described.