The force of gravity pulling down on the barbell is 756 newtons (N) How many
newtons of force are exerted by the
weightlifter to hold the barbell up?

Explanation:

The same. The force down (the weight of the barbells) is counter balanced by the weight up ( a person holding the barbells). A little later on, you are going to draw force diagrams showing that these two forces are drawn acting in opposite directions.

You can satisfy yourself by drawing a box and putting 1 arrow pointing up on the bottom and labeling it 756 up and another arrow on the top of the box pointing down and labeling it 756. They balance.