I had a quick search but couldn't find the answer I was looking for.

I'm booking a weekend trip in March for my mum and dad, flying GLA-LHR return. When I select the flights the outbound says £35 (HBO) and £45 (+luggage), so I select the £45. I make that £90 for them both, essentially. It then updates the prices for the inbound flights.

Then choosing inbound, it's £54 (+luggage) for the return flight. So I make that £99 each, so £198. However on the following page where it displays a summary of the chosen flights it says £215, so £17 more than I was expecting. I know it's only £17 but I'm unaware where this extra £17 is coming from. Does anyone have any idea?

Thanks in advance.