Larry weighs 300 N at the surface of the earth. what is the weight of the earth in the gravitational field of Larry?

Question

-force= GMm/d^2
would i set it up like force= (9.8m/s^2)(300 N)?

an astronaut lands on a planet that has twice the mass as earth and twice the diameter. how does the astronaut weight differ from that on earth? (this one i don't get still)

if the moon pulls the earth as strongly as the earth pulls the moon, why doesnt the earth rotate around the moon, or why don't both rotate around a point midway between them?
-the earth doesnt rotate around the moon because the moon is not center of gravity and they both don't rotate around a point midway between them because of the center of gravity.