Force acting on \(q\) due to \(\mathrm{Q}_{1}\) and \(\mathrm{Q}_{5}\) are opposite direction, so cancel to each other. Force acting on \(q\) due to
\(\mathrm{Q}_{3}\) is \(\mathrm{F}_{3}=\frac{1}{4 \pi \varepsilon_{0}} \frac{q Q_{3}}{R^{2}}\)
Force acting on \(q\) due to \(Q_{2}\) and \(Q_{4}\)
Resolving in two component method:
(i) Vertical Component: \(\mathrm{Q}_{2} \operatorname{Sin} \theta\) and \(\mathrm{Q}_{4} \operatorname{Sin} \theta\) are equal and opposite direction, so they are cancel to each other.
(ii) Horizontal Component: \(\mathrm{Q}_{2} \operatorname{Sin} \theta\) and \(\mathrm{Q}_{4} \cos \theta\) are equal and same direction, so they can get added.
\(F_{24}=F_{2 q}+F_{4 q}=F_{2} \cos 45^{\circ}+F_{4} \cos 45^{\circ}\)
\(F_{24}=\frac{1}{4 \pi \varepsilon_{0}} \frac{q Q_{2}}{R^{2}} \cos 45^{\circ}+\frac{1}{4 \pi \varepsilon_{0}} \frac{q Q_{ 4}}{R^{2}} \cos 45^{\circ}\)
Resultant net force \(\mathrm{F}\)

\(\mathrm{F}=\mathrm{F}_{3}+\mathrm{F}_{24}+\mathrm{F}_{15}\)
\(\cos 45^{\circ}=\frac{1}{\sqrt{2}}\)
\(\ \mathrm{F} =\frac{q \mathrm{Q}}{4 \pi \varepsilon_{0} \mathrm{R}^{2}}\left[1+\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{2}}\right]\)
\(=\frac{1}{4 \pi \varepsilon_{0}} \frac{q \mathrm{Q}}{\mathrm{R}^{2}}\left[1+\frac{2}{\sqrt{2}}\right]\)
\(\mathrm{F} =\frac{1}{4 \pi \varepsilon_{0}} \frac{q \mathrm{Q}}{\mathrm{R}^{2}}[1+\sqrt{2}] \mathrm{N} \)
Vector form:
\(\overrightarrow{\mathrm{F}}=\frac{1}{4 \pi \varepsilon_{0}} \frac{q \mathrm{Q}}{\mathrm{R}^{2}}(1+\sqrt{2}) \mathrm{N} \hat{i}\)