Add
15xy,-6xy,-3xyand4xy
The given pairs of terms 15xy,-6xy,-3xyand4xy are like terms.
So, adding the numerical coefficient of each term.
The sum
=15xy+(-6xy)+(-3xy)+4xy=15xy+4xy+(-6xy)+(-3xy)=19xy+(-6xy)+(-3xy)=19xy-6xy-3xy=19xy-9xy=10xy
3x3y2+2x2y+15xy by 3xy