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Foriginal = 700 = G m M / r^2
700 = G 200 M / R^2 = 200 G M / R^2
so G M/R^2 = 7/2
then later
F = G 800 M/ (4R)^2 = (800/16) G M/R^2
= (800/16) * (7/2) Newtons