We have been given two functions:
 and
 and 

Question says that graph of 
 and
 and 
 are symmetric about a line. Now we have to find that line of symmetry.
 are symmetric about a line. Now we have to find that line of symmetry.
So let's graph both equations to find that line of symmetry.
we can plug any number for x like -3, -2, -1, 0, 1, 2, ...
for x=2, we get 
 
 
So we get point (2,4)
Same way we can find more point then graph those points and join them
We can repeat same process for other equation 

So the graph will look like the attached picture.
From graph we can see that both lines are mirror image that is symmetric about the y-axis .
Hence final answer is that line of symmetry is y-axis. or you can say x=0.