Question

Given: Q1 = 3.0 × 10-5 C

Answer 1

F=KQ1Q2/R2
F=9 x 10^9 x 3 x 10^-5 x 4 x 10^-5 / 9
F=12 x 10^-1
F=1.2 N

Answer 2

$F=k\dfrac{Q_1Q_2}{r^2}= \\ \\ =9\cdot 10^9\cdot \dfrac{3\cdot 10^{-5}\cdot 4\cdot 10^{-5}}{9}=...$

You just do the calculations.