`a)P(x)=-3x^3+2x^2+2x^3+x-1`
`=(-3x^3+2x^3)+2x^2+x-1`
`=-x^3+2x^2+x-1`
`Q(x)=x^3-3x^2-x+2x^2-3`
`=x^3+(-3x^2+2x^2)-x-3`
`=x^3-x^2-x-3`
`b)M(x)=(-x^3+2x^2+x-1)+(x^3-x^2-x-3)`
`=-x^3+2x^2+x-1+x^3-x^2-x-3`
`=(-x^3+x^3)+(2x^2-x^2)+(x-x)+(-1-3)`
`=0+x^2+0-4`
`=x^2-4`
`N(x)=(-x^3+2x^2+x-1)-(x^3-x^2-x-3)`
`=-x^3+2x^2+x-1-x^3+x^2+x+3`
`=(-x^3-x^3)+(2x^2+x^2)+(x+x)+(-1+3)`
`=-2x^3+3x^2+2x+2`
`c)M(x)=x^2-4=0`
`=>x^2=4`
`=>x=2`