We can also think of this problem as f(x) + g(x). Therefore, all we need to do is add the two functions together.
x + 4 + 3x^2 - 8 || Write it out!
3x^2 + x + 4 - 8 || Rearrange in order of decreasing exponents. No need to combine and rearrange all at once!
3x^2 + x - 4 || Combine like terms!
Hope this helps!! :)