When we reflect every point over the x axis...
- S(2, -4) becomes S ' (2, 4)
- T(9, -4) becomes T ' (9, 4)
- U(9, -1) becomes U ' (9, 1)
- V(2, -1) becomes V ' (2, 1)
The rule you use is

The x coordinate stays the same while the y coordinate flips in sign (in this case from negative to positive)