Can you help me subtract intervals? I was reading my abstract math textbook and they subtracted
$[3, 6] - [4, 8) = [3, 4)$. I was wondering if someone could write out how they got to $[3, 4$). I looked at wikipedia and it said I should go 
$[a, b] - [c, d] = [a-d, b-c]$. When I did this, I got $[-5, 2)$. I would be thankful for an explanation-- the book doesn't explain so it's probably really obvious-- but I don't know.

You are looking at two different definitions of $A-B$:
Set difference: $A - B = \{ x\in A \, \mid \, x \notin B \}$ which in this case gives $$[3,6]−[4,8) = [3,4)$$
Interval arithmetic: $A - B = \{ x-y \in \mathbb{R} \, \mid \, x\in A,  \,y \in B \}$ which in this case gives $$[3,6]−[4,8) = (-5,2]$$
