Question

what happens to the force gravitation between two objects, if a) the mass of one object is doubled b) the distance between the object is doubled

Answer 1

You can refer question no. 6 for your answer.

Answer 2

we know that force=GMm/r2
it tells us that force is directly proportional to masses and inversely proportional to r
when mass is double then force of gravity is double.
when distance between objects r is double then force of gravity is half.
hope it helps