Answer
See explanation.
Work Step by Step
(a) $x=f(x)$ , $2 x=g(x)$ are increasing everywhere; the difference is then decreasing everywhere.
(b) $g(x)=x$ and $f(x)=x$ are increasing everywhere; the difference is then constant everywhere.
(c) $g(x)= x$ and $f(x)=2 x$ are increasing everywhere; the difference $(-$$g+f)(x)=x$ is then increasing everywhere