The top of a mountain has an altitude of 12,221 feet above sea level and the bottom of a valley nearby is at 138 feet below sea level. Answer each of the following questions, including units with all answers.
A. Find the difference between these two elevations.
B. Round your answer from part (a) to the nearest 10 feet.
C. Round your answer from part (a) to the nearest 100 feet.
D. Round your answer from part (a) to the nearest 1000 feet.
E. Round your answer from part (a) to the nearest 10,000 feet.