What is the gravitational field strength of a planet where the weight of a 60kg astronaut is 300N?

What is meant by gravitational field strength ?

The gravitational field strength at the surface of a certain planet is g. Which of the following is the gravitational field strength at the surface of a planet with twice the radius and twice of the mass?

In a gravitational field, at a point where the gravitational potential is zero

What will the weight of man of 60 kg in the moon ?

Where is the gravitational field zero and where is the gravitational potential zero, in case of Earth?