Okay, haven't done physics in years, let's see if I remember this.
So Coulomb's Law states that
so if we double the charge on 
and double the distance to 
we plug these into the equation to find
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So we see the new force is exactly 1/2 of the old force so your answer should be
if I can remember my physics correctly.
So Coulomb's Law states that
<span>
So we see the new force is exactly 1/2 of the old force so your answer should be