12x-12y it's distributive property I don't get it
Distributive Property basically means that you have an expression, and every value in that expression is multiplied or divided by the same thing.
So for your example, you divide everything by 12. But since it is an expression, not an equation, you can't get rid of the 12 and be done. You have to put it somewhere so that it remains in the equation. Thus, 12(x-y)