$$ f =(6.67 \ times10^{-11} \ text {n $ \ cdot $ m}^2/\ text {kg}^2)\ frac {3 \ times700 \ text {kg}}}}}} {(0.140 \ text {m})^2} =\ boxed {3} \ boxed {-36 \ n}} $$
$$ f =(6.67 \ times10^{-11} \ text {n $ \ cdot $ m}^2/\ text {kg}^2)\ frac {3 \ times700 \ text {kg}}}}}} {(0.140 \ text {m})^2} =\ boxed {3} \ boxed {-36 \ n}} $$