The gravitational force of attraction between two objects is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them.
Where,
G = Gravitational Universal Constant
M = Mass of the Planet
m = Mass of the object
r = Distance
Therefore the amount of force exerted by the first object on the second object is equal to the amount of the force exerted on the second object by the first.
The gravitational force exerted by Larry on the Earth is same as the force exerted on Larry by the Earth.
That is 300N.