In the author's opinion, why is attitude the most important fitness level factor to consider? (

That's up to you because you have to go through the book to see their expressions

Since the pully is a simple machine so the mechanical advantage is a 1

Gravity, from the center of mass of the box, extending downward normal force, from the floor under the box, extending upward, equal to gravity push force, acting at a point on the box, extending in the direction of motion friction, acting at any point on the box directly opposite the push, extending directly opposite to the motion