F = 9 \cdot 10^{9} N m^{2} C^{- 2} \frac{10 C \cdot 20 C}{(5 \cdot 10 m)^{2}} = \underline{\underline{- 7 \cdot 10^{4} N}}

${F = \mathrm{9 \cdot 10^9\, Nm^2C^{-2} \frac{10\, C \cdot 20\, C}{ (5\cdot 10\,m)^2} = \underline{\underline{-7 \cdot 10^4\, N}}}}$

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