Pretty much every time it asks for the abasloute value it just asks how much to get the zero on the number line. It will ALWAYS be positive. For example -5 will be 5 to get to zero on the numberline. Same thing with a positive 5.
If Mr. Wilson has 12 more students than Mr. Star, whatever Mr. Star has (x) plus 12, should equal 30. That would make x, or the amount of students Mr. Star has, 18. This answer is included in option C.