First, coordinate Q is (-5,2) and Q' is (6,2). First, we know that this is a horizontal reflection becuase only the x-values change. This means that the line of reflection will be x=some value. I think the best way to go about this is to find the midpoint of Q and Q' using the formula: M=(x1+x2/2,y1+y2/2)
Q is the first point and Q' is the second point
M=(-5+6/2,2+2/2)
M=(1/2,4/2)
M=(1/2,2)
Since we know the y-values of Q, Q', and the midpoints are all 2, then the line of reflection would be x=1/2
Hope this helps