Final answer:
The temperature at 30,000 feet compared to ISA conditions is -45°C. This follows the ISA standard lapse rate of -6.5°C per 1,000 meters up to 11,000 meters.
Step-by-step explanation:
The temperature at 30,000ft, compared to ISA (International Standard Atmosphere) conditions, is -45°C. The ISA defines a standard temperature lapse rate of about -6.5°C per 1,000 meters (or approximately -2°C per 1,000 feet) up to the altitude of 11,000 meters (36,089 feet), which is commonly referred to as the tropopause. At sea level, the ISA standard temperature is 15°C. By the time you reach 30,000 feet (approximately 9,144 meters), the temperature would have decreased by -45°C, making the correct answer C. -45°C.