`a)`
`M+(5x^2-2xy)=6x^2+9xy-y^2`
`=>M+5x^2-2xy=6x^2+9xy-y^2`
`=>M=6x^2+9xy-y^2-5x^2+2xy`
`=>M=(6x^2-5x^2)+(9xy+2xy)-y^2`
`=>M=x^2+11x-y^2`
`b)`
`M-(x^3y^2-x^2y+xy+xy)=2x^3y^2-3/2xy`
`=>M-(x^3y^2-x^2y+2xy)=2x^3y^2-3/2xy`
`=>M-x^3y^2+x^2y-2xy=2x^3y^2-3/2xy`
`=>M=2x^3y^2-3/2xy+x^3y^2-x^2y+2xy`
`=>M=(3x^3y^2+x^3y^2)+(-3/2xy+2xy)-x^2y`
`=>M=4x^3y^2+1/2xy-x^2y`
`c)`
`(-2x^3+x^2-1/3x-9)-M=2x^3-3x^2-2/3x`
`=>M=-2x^3+x^2-1/3x-9-2x^3+3x^2+2/3x`
`=>M=(-2x^3-2x^3)+(x^2+3x^2)+(-1/2x+2/3x)-9`
`=>M=-4x^3+4x^2+1/6x-9`
