已知A=5x的平方y-3xy的平方+4xy,B=7xy的平方-2xy+x的平方y,若A+B+2C=0,求C-A是多少?

A=5x^2y-3xy^2+4xy
B=7xy^2-2xy+x^2y
2C=-A-B
2C-2A=-3A-B=-15x^2y+9xy^2-12xy-7xy^2+2xy-x^2y=-16x^2y+2xy^2-10xy
C-A=-8x^2y+xy^2-5xy