Ms nickel has a jar of candy on her desk. jessica thinks there are 3,498 piece of candy in the jar there are actually 4,182 pieces. what is the difference between jessica's guess and the actual number of pieces of candy?

This is quite easy. So we know that difference is a key word to subtract. So this means we need to subtract 3,498 from 4,182. 4,182 - 3,498 is 684. Let's put it like this:
The difference between Jessica's guess and the actual amount of candy in the jar is 684 pieces off from the actual amount.
Hope this helped! :)

The first option would be correct if it were one half and not one