Sometimes these fuel questions can be a little confusing ... the standard fuel requirement for a sector includes the following fuel calculations:

TRIP + CONTINGENCY + ALTERNATE + FINAL RESERVE

Sometimes in these questions they simply talk about RESERVE requirements ... I would then have to assume that they mean (ALTERNATE + FINAL RESERVE ..... Contingency effectively can be ignored once airborne).

Faced with some of these fuel questions just take the data offered and keep it as simple as possible ... hence at the half way point you have used 40gals....we will have to assume we will use another 40gals to get to our dest ... which leaves 13 gals .... reserves not intact!!