Answer:
10 lb of force are needed to lift the rock if the distance from the fulcrum is 6 feet.
Explanation:
From the given graph it is clear the curve passing through the point (1.5,40), (2,30), (2.5,24), (3,20) and (4,15).
These points satisfy by the equation

where, x is the distance in feet from the fulcrum and y is needed force in pounds.
Put x=6 in this equation,

Therefore, 10 lb of force are needed to lift the rock if the distance from the fulcrum is 6 feet.