Refer to figure.
After 25 minutes the remaining fuel is 120 lb. This means that the fuel that has been consumed is:

• Consumed fuel at 25 min = 200 lb - 120 lb = 80 lb

80 lb of fuel have been consumed within 25 minutes. This means that fuel consumption is:

• Fuel Flow = 80 lb / 25 min = 3.2 lb/min

The aircraft should land with its final reserve fuel and its alternate fuel, which is 30 lb + 40 lb = 70 lb. This means that fuel at landing should be at least 70 lb and the maximum fuel consumed can be:

• Totel fuel that can be used = 200 lb - 70 lb = 130 lb

The aircraft has already consumed 80 lb after 25 minutes, which means that the rest of the fuel that can be consumed is:

• Remaining fuel that can be used = 130 lb - 80 lb = 50 lb

Since the remaining fuel that can be consumed is 50 lb and the calculated fuel flow is 3.2 lb/min, the aircraft is able to fly for:

• Remaining flight time = 50 lb / 3.2 lb/hr = 15.6 min