Which of the following changes to the earth-sun system would reduce the magnitude of the force between them to one-fourth the value found in part a?

reduce the mass of the earth to one-fourth its normal value.
reduce the mass of the sun to one-fourth its normal value.
reduce the mass of the earth to one-half its normal value and the mass of the sun to one-half its normal value.
increase the separation between the earth and the sun to four times its normal value.

part a was:

consider the earth following its nearly circular orbit (dashed curve) about the sun. the earth has mass mearth=5.98