5) What does QRST → Q'R'S'T' mean?

QRST becomes Q prime, R prime, S prime, T prime.

Step-by-step explanation:

Any figure that is rotated, translated or reflected on the corrdinate plane is considered a prime (as long as it is congruent (the same as, or equal to) with the original). The apostrophe stands for prime.

Ex. If you reflect triangle ABC across one of the axes, the original triangle will continue being ABC, while the reflection would be A' B' C' (or A prime, B prime, C prime). I hope this helps :)