So this is the info that's given to us:
m1 = 4.87 x 10^24 kg
m2 = 4.87 x 10^24kg
F = 2.58 x 10^3 N
Now we can use this equation to solve:

You may be asking what g is. Well, it is equal to 6.67x10^-11 m3 /kg s2. G is gravitational constant. So :
As you can see we only have one variable, so we solve for r!

I hope this helps you out. I remember when I was first learning Newton's law
of universal gravitation and I had some trouble. But with some practice, I got better. =)