Okay so for the part of the first question I find confusing is that from question #1 you are given pH and from there you can calculate [H+] and [CH3COO-] which are both X.
Then, notice that in question #2 you're not given the Ka, but expected to calculate it with the X from question #1.
So the first wuestion I had was this
1. Use the initial pH of the acetic acid solution to find the initial [H3O+] and initial [CH3COO]-(2)
Initial pH = 2.58
pH = -log[H+]=2.58
= [H+] = 10^-2.58
= 2.63*10^-3 m
so What I would do is (2.63 x 10^-3)/0.1 = 0.0263 or 2.63 x 10^-2
Would that be the correct answer then?