-204 + 418 is 214 ft
-56 - 214 is -270 ft
I believe these should be correct.
A. Note that you are subtracting 5280 with -282
5280 - (-282) = 5280 + 282 = 5562
Denver is 5562 feet taller than death valley
B. your elevation should be ~ 0 feet if you are standing near the ocean, for ocean level is 0 feet.
hope this helps
This is the diffiarence of two perfect squares. this should be memorised, but if not here it is
a^2-b^2=(a-b)(a+b)
so 16^2-81=16^2-9^2
so the answer is (16-9)(16+9)