Hey there!
If it’s ABOVE sea level it usually means it’s BIGGER than 0 and if you’re BELOW sea level it usually means it’s SMALLER than 0.
Positives turns into negatives and negatives turns into positive
Above opposite is Below and Below opposite is Above
Thus, this means “100 feet ABOVE sea level” will probably -100 feet BELOW sea level”
Good luck on your assignment and enjoy your day!
~Amphitrite1040:)