What determines the gravitational force between earth and the moon

The gravitational forces between the earth and moon at an average distance between them may be expressed as (F)

Explanation:

Both the mass of the earth and the moon are doubled.The distance between the center of two are doubled.So both masses are doubled and the distance is halved.

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parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.

substitution is the answer in this case