e in this case just represents a variable, I believe.
with this, unless we are given a solution to e or x, the answer might not be accurate. Assuming that e does not = a fraction or decimal, the answer to this is 2e, e^2, e^3. However, since we don't know the solution to x or e, I'm thinking that the answer to this can be put any way as long as 2e, e^2, and e^3 are put in that order. I wish you the best of luck, I'm off to find out more about this problem!