Based on jack's upper body pretests, he wants to start at 65% 1rm for the bench press/dumbbell workout, 75% 1rm for lat pulldowns, and 50% 1rm for biceps curls. how much weight should he use for each?

In weightlifting, "One-Repetition Maximum" is the maximum weight that you can lift in a single repetition (not more) for a given exercise.

By this number, you can figure out, by using algorithms and calculations how many repetitions and how much weight he should lift.

I did not find the exercise to see Jack's pretests, but if you have his 1RM, you calculate how much weight he should lift in each exercise using the given percentages.