So it’s basically given you the coordinates as y=f(x)
Now take any two coordinates and find slope of the line joining them
If they all come same (which they will as 1/2)
Then f(c) represents a line
Now take any point and slope is 1/2
So let’s take (0,-6)
y+6=(1/2)(x)
=> 2y+12=x
=>y=(x-12)/2
=> f(x)= (x-12)/2