a
\(\overrightarrow {\text{E}}  = \frac{{{\text{k}}{{\text{q}}_1}}}{{{\text{r}}_1^3}}{\overrightarrow {\text{r}} _1} + \frac{{{\text{k}}{q_2}}}{{{\text{r}}_2^3}}{\overrightarrow {\text{r}} _2}\)

\( = {\text{k}} \times {10^{ - 6}}\left[ {\frac{{\sqrt {10} }}{{10\sqrt {10} }}( - \widehat {\text{i}} + 3\widehat {\text{j}}) + \frac{{( - 25)}}{{125}}( - 4\widehat {\text{i}} + 3\widehat {\text{j}})} \right]\)

\( = \left( {9 \times {{10}^3}} \right)\left[ {\frac{1}{{10}}( - \widehat {\text{i}} + 3\widehat {\text{j}}) - \frac{1}{5}( - 4\widehat {\text{i}} + 3\widehat {\text{j}})} \right]\)

\( = \left( {9 \times {{10}^3}} \right)\left[ {\left( { - \frac{1}{{10}} + \frac{4}{5}} \right)\widehat {\text{i}} + \left( {\frac{3}{{10}} - \frac{3}{5}} \right)\widehat {\text{i}}} \right]\)

\( = 9000\left( {\frac{7}{{10}}\widehat {\text{i}} - \frac{3}{{10}}\widehat {\text{j}}} \right)\)

\( = (63\widehat {\text{i}} - 27\widehat {\text{j}})(100)\)