If f(x) = x^2 - 2x + 4, find f(3m - 4) + 3.
Simply add it to whatever you get for $\displaystyle {\color{blue}f(3m-4)}$ .
So: $\displaystyle {\color{blue}f(3m-4)} + {\color{red}3} = {\color{blue}9m^2-30m+} \underbrace{{\color{blue}28} + {\color{red}3}}_{\text{Add}} = 9m^2 - 30m + 31$
as what the other posters got.