If you know your 1RM back squat (or approximately), use 65-75% for the back squats. Use the same weight across all sets. How do you know it’s the right weight? It should be tough around rep 4 or 5, and you should really fight for that 8th rep. Rest between sets should be no LESS than 2 minutes.
The metcon consists of air squats and sprints. Do 10 air squats and then sprint as fast as possible for 100m. This should be a straightaway, not a turn around. Coaches will time each round for you – your score is the fastest time, but also record the other 4 times. Rest should be about 1:30-2:00, but start each interval as a group.

Strength

Back squat
3 x 8

Conditioning

5 rounds:
10 air squats
sprint 100m
rest 1:30-2:00