The problem uses the concept of Lever and Fulcrum.
The tire is placed on one end of the bar and the man applies force on the other end. Rock is placed 2 feet from the tire. The total length of the bar is 11 feet. This means, the distance between man and the rock is 9 feet as shown in the mage below.
According to principle of Level and Fulcrum, the product of force and distance from the level must be same on both sides.
So, product of force applied by man and 9 must be equal to the product of 2 and weight of tire.
We can set up the equation as:
9x = 2(108)
Dividing both sides by 9, we get the values of x to be:
x = 24 pounds
Therefore, the man must exert 24 pounds of force to lift the 108 pound tire.
