(7x+2+8x^4)-(2x-5-8x^4)+(3x+5x^4)
(7x+2+8x^4)-(2x-5-8x^4)+(3x+5x^4)(5x+7+16x^4) + (3x+5x^4)8x + 7 + 21x^4
(7x+2+8x^4)
-2x+5+8x^4
(5x+7+16x^4)+(3x+5x^4)
=8x+7+21x^4