Final answer:
To reflect a point across the x-axis, change the sign of the y-coordinate while keeping the x-coordinate the same.
Step-by-step explanation:
To reflect a point across the x-axis, we simply change the sign of the y-coordinate while keeping the x-coordinate the same. In this case, the rectangle with vertices P(2,4), Q(8,4), R(2,-2), and S(8,-2) would be reflected to P'(2,-4), Q'(8,-4), R'(2,2), and S'(8,2), respectively.