don't show 45 min hint, if min is 15, 20 or 40

does not show 45 min hint only if min is 30
example: [telling_time_2.html?problem=set-hands-20-minute](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/telling_time_2.html?debug&problem=set-hands-20-minute)