DSE 2020 Question 48: Sets, relations and functions

If $f,g:\mathbb{R}\to\mathbb{R}$ are defined by $f(x)=0$ if $x$ is rational and $f(x)=x$ if $x$ is irrational, and $g(x)=0$ if $x$ is irrational and $g(x)=x$ if $x$ is rational, then $h:\mathbb{R}\to\mathbb{R}$ given by $h(x)=f(x)-g(x)$ is