take the two denominators: 8y and 6xy
and try to make them equal to each other with the simplest operations so if you multiply 3*8 and 4*6, you get 24, which is the same:
3(8y) =? 4(6xy)
this is 24y = 24xy, now the only thing different is the x:
3x(8y) = 4(6xy)
and this simplifies to
24xy
you could also do
6x(8y) = 8(6xy) = 48xy, but this isn't the Least Common denominator. 24xy's the least common denominator.
I'm bad at explaining this, if you have a specific question anymore ask
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"Strong am I with the Force, but not that strong.
Twilight is upon me, and soon, night must fall.
That is the way of things. The way of the Force."
--Yoda