It is given that, The Sun exerts a gravitational force of 29.9 N on a rock that's located in a river bed here on Earth. We need to find the gravitational force the rock exert on the Sun. It is a case of Newton's third law of motion which states that the force acting from one object to another is equal to the force acing from second object to the first object and the two forces must be in opposite direction. Hence, the gravitational force the rock exert on the Sun is same i.e. 29.9 N.
