because we all share the same mind and because that mind wrote the question, it also chose the answers.
notice it says ' between 12 and 5.' and not ' between 5 and 12.'
and with all that adding earlier your mind is in a simple mathematics mode.
the 5,7,12 combination is quite distinct, so its very likely your brain sees 12 minus 5 and thus gets 7.
if you dont get 7 then you either thought about it, or you're a bit thick.
3 and red are linked, and you mind is happy to see them almost as one. red has three letters and sounds similar. and also its one of 3 primary colours - and probably the most common.
and hammer is probably the most common tool, and one that we can all use and name - even girls.
so its a simple test of your brain to make sure all circuits are functioning. if you didnt choose 7, red, hammer you most likely didn't do it instinctively but tried to be a smart arse and come up with something different. like pi^2/2, green polka dots, hi pressure water hose.
but you can remember fighting the urge to say red hammer right...?
____
Tony