Hello, thank you for taking the time to post your question!
In this scenario (f + g)(x) means adding the two functions together, so you want to take f(x) + g(x)
f(x) + g(x) = -6x – 1 + 4x^2
=4x^2 – 6x - 1
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)
Steve S.
03/29/14