The first thing you need to do, is put the like terms in order. So it would be, (-3x)-2x+7x-15xy+4xy.(basically the 4xy and 2x switch places, just take the sign that's in front of them with them.) Now you would combine the like terms. ((-3x)-2x+7x)-(15xy+4xy). Simplified, the new equation is 2x-19xy.
