Answer:
R prime S prime T prime
Explanation:
ΔRST is named for its three vertices, R, S, and T. When the image is created, those vertices become R', S', and T'.
The three vertices can be referenced in any order to name the image triangle, However, if you want to claim congruence to the original, in general, you will need to name them in the same order as the original: ΔR'S'T'.