The sum function [tex] (f+g)(x) [/tex] is defined exactly as the sum of the two functions:
[tex] (f+g)(x) = f(x)+g(x) [/tex]
So, you simply have to sum the expressions:
[tex] (u+v)(x) = u(x)+v(x) = (x+3)+(9x-4) = 10x-1 [/tex]
