Final answer:
The altitude of the plane after Tessy's descent and subsequent ascent is "4100 feet, option C".
Step-by-step explanation:
After descending 2000 feet, the plane's altitude is initially reduced by this amount.
Then, it ascends 4 times the descent, which is 4 * 2000 = 8000 feet. Combining the descent and ascent, the net change in altitude is 8000 - 2000 = 6000 feet.
Therefore, the final altitude is the initial altitude minus the net change, resulting in 6000 feet. Thus, the plane's altitude is "4100 feet".