A=2x2-3xy+2y2,B=2x2+xy-3y2
A+B=2x2-3xy+2y2+2x2+xy-3y2
=4x^2-2xy-y^2
2A-3B =4x2-6xy+4y2-(6x2+3xy-9y2)
=-2x^2-9xy+13y^2