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