Answer
$f(x)=-\dfrac{x}{4}+\dfrac{5}{4}$
Work Step by Step
We need to find the line equation by using two points such as: $(1,1); (2,-3)$
$\dfrac{y-1}{-3-1}=\dfrac{x-1}{2-1}$
This gives: $y-1= -4x+4$
or, $x=\dfrac{-y+5}{4}=-\dfrac{y}{4}+\dfrac{5}{4}$
Thus, we have the linear equation for the function $f(x)$ is $f(x)=-\dfrac{x}{4}+\dfrac{5}{4}$
