[tex] \large \boxed{(f + g)(x) = f(x) + g(x)}[/tex]
The property above is distribution property where we distribute x-term in the function.
Substitute both f(x) and g(x) in.
[tex] \large{ \begin{cases} f(x) = 2 {x}^{2} - x - 6 \\ g(x) = 4 - x \end{cases}} \\ \large{f(x) + g(x) = (2 {x}^{2} - x - 6) + (4 - x)} \\ \large{f(x) + g(x) = 2 {x}^{2} - x - 6 + 4 - x}[/tex]
Évaluate/Combine like terms.
[tex] \large{f(x) + g(x) = 2 {x}^{2} - 2x - 2} [/tex]
The function can be factored so there are two answers. (Both of them work as one of them is factored form while the other one is not.)
[tex] \large{(f + g)(x) = 2 {x}^{2} -2x -2}[/tex]
Alternative
[tex] \large{(f + g)(x) = 2({x}^{2} -x - 1)}[/tex]
Answer
Both answers work. The second answer is in factored form.
Let me know if you have any doubts!