The slope is -2. In context to this problem, the candle will burn away 2cm of its length every hour.
I think you should do this equation
So. let's say the numbers are "a" and "b"
whatever they're, we know a + b = 56
let's say the larger one is "b", so 3 times the smaller is 3*a or 3a
now, 12 less than that, is 3a - 12
and the larger is that, so b = 3a - 12
so

solve for "a", to see what the smaller one is
what's b? well, b = 56 - a