For any value of e, (the edge length), just cube it to get the volume. Easy
V(-2) = -8 V(-1) = -1 V(0) = 0 V(1) = 1 V(2) = 8 V(3) would be 27...etc
It doesn't make sense to use a negative or zero value for e (since you can't have a length like that), so technically there should be a restriction of e > 0.
To find the edge length given the volume, we would just solve for e.
V = e³ Take the cube root of each side... ∛V = ∛e³ ∛V = e
Yes for the first one, yes for the second one, and yes for the third one although your subtraction equation had the wrong year (its not 1847 its 1846) but the answer was right, 65.