Moist adiabatic lapse rate is the rate at which a saturated air parcel cools as it rises. When air rises and becomes saturated, condensation releases latent heat, which slows the cooling compared to dry air. That’s why the moist rate is smaller than the dry rate (the dry rate is about 3°C per 1000 feet). In many aviation references, the moist adiabatic lapse rate is approximated around 2.5°C per 1000 feet, so the stated value of 2.5 aligns with that common estimate. Remember, the exact rate can vary with temperature and moisture, typically ranging roughly from about 1.5 to 3°C per 1000 feet.

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.

Knots are nautical miles per hour, while miles per hour use statute miles. Since 1 nautical mile is about 1.15078 statute miles, 1 statute mile is 1/1.15078 ≈ 0.868976 nautical miles. So 1 mile per hour equals about 0.868976 nautical miles per hour, i.e., roughly 0.87 knots. A handy way to remember this is that 1 knot is about 1.15 mph, so converting mph to knots is roughly dividing by 1.15 or multiplying by 0.87. Therefore, 1 mph equals about 0.87 knots.

To convert Celsius to Fahrenheit you scale the temperature by 9/5 (which is 1.8) and then add 32 to account for the different zero points. The correct expression is Fahrenheit equals 9/5 times Celsius plus 32, or F = (9/5) × C + 32, often written as F = 1.8C + 32. The 32 is the Fahrenheit value at 0°C, so you first adjust the size of a degree, then shift the zero point. If you add 32 before multiplying, you’d effectively apply the offset to the scaled value as well, leading to an incorrect result. Using 2 as the multiplier is not accurate because a 1°C change equals 1.8°F, not 2°F. The form that uses (Celsius − 32) × 5/9 is the inverse direction (it converts Fahrenheit to Celsius) and doesn’t give Fahrenheit from Celsius.