${{E}_{2}}=9\times {{10}^{9}}\times \frac{4\times {{10}^{-9}}}{{{(4\times {{10}^{-2}})}^{2}}}={{10}^{4}}\frac{N}{C}$
${{E}_{3}}=9\times {{10}^{9}}\times \frac{12\times {{10}^{-9}}}{{{(6\times {{10}^{-2}})}^{2}}}=3\times {{10}^{4}}\frac{N}{C}$
${{E}_{2,3}}={{E}_{3}}-{{E}_{2}}=2\times {{10}^{4}}\frac{N}{C}$
${{E}_{t}}=\sqrt{E_{1}^{2}+E_{2,3}^{2}}\Rightarrow \sqrt{5}\times {{10}^{4}}=\sqrt{E_{1}^{2}+{{(2\times {{10}^{4}})}^{2}}}\Rightarrow {{E}_{1}}={{10}^{4}}\frac{N}{C}$
${{E}_{1}}=9\times {{10}^{9}}\times \frac{\left| {{q}_{1}} \right|}{r_{1}^{2}}\Rightarrow {{10}^{4}}=9\times {{10}^{9}}\times \frac{\left| {{q}_{1}} \right|}{(3\times {{10}^{-2}})2}\Rightarrow {{q}_{1}}={{10}^{-9}}C=1nC$