(1)

Add or Subtract

(9x^4+7x^2-6x-15)+(3x^3-7x^2+6x-15

(2)

Add or Subtract

(9x^3+x^2-x-13)-(9x^3+x^2-x-13)

(3)

Add or Subtract

(9m^4n^2-13m^3n^3+11m^2n^4)+(-4m^2-n^4-3m^4n^2-m^3n^3)

(4)

Add or Subtract

(22x^3y^9-21x^6y^4-7x^8y^2)-(22x^3y^9-21x^6y^4-7x^8y^2)

(5)

Find the missing polynomial

(2x^3-4x^2-7x+19)+ ? =x^2+3x+24