first we need to get rid of the ( ) so that we can see what the question really says
(3x³-5x² - 7+ 4x4) + (9x4 - 10x² - 5x³ + 3)
= 3x³-5x²-7+4x⁴+9x⁴-10x²-5x³+3
now all we need to do is add up the numbers with the same x's
3x³-5x²-7+4x⁴+9x⁴-10x²-5x³+3
= 13x⁴-2x³-15x²-4
