Question is talking about reflection of the triangle JKL to triangle J'K'L'. But the picture of reflection is missing.
So I will explain with an example.
Say the original coordinate of point K is (5,2).
Now we see that K(5,2) is changed into K'(-5,2)
Notice that only x-coordinate 5 is changing to -5.
When only x-coordinate changes then that means reflection is happening about y-axis
If only y-value changes then it occurs due to reflection about x-axis.
You can use these results in original picture to find the correct answer.