Step-by-step explanation:
[tex]f(x) = 3x - 9 \\ plug \: x = 5 \\ f(5) = 3 \times 5 - 9 \\ \hspace{22 pt} = 15 - 9 \\ \hspace{15 pt}\huge \purple{ \boxed{f(5)= 6}} \\ [/tex]
