Given,
The force applied by each person who is pushing the object, F=50 N
The frictional force, f=20 N
The frictional force is the force that opposes the motion of the object. As the people are pushing the object to the right, the frictional force will be directed to the left. And as the force with which people are pushing is greater than the frictional force, the net force will also be directed towards the right.
The net force is given by,
On substituting the known values,
Therefore the net force on the object is 80 N to the right.
Thus the correct answer is option 4.