2) (11х^4+21x^3-43)+(60-19x^3-7x^4)=11х^4+21x^3-43+60-19x^3-7x^4=

=4x^4+2x^3+17

4) (-73+17x+19x^3)-(-18x^3-39x+50)=-73+17x+19x^3+18x^3+39x-50=

=37x^3+56x-123