a
\(\left|\overrightarrow{\mathrm{F}}_1\right|=\mathrm{F}\)

\(\left|\overrightarrow{\mathrm{F}}_{\mathrm{R}}\right|=\left|\overrightarrow{\mathrm{F}}_2\right|=3 \mathrm{~F}\)

\(\mathrm{~F}_{\mathrm{R}}^2=\mathrm{F}_1^2+\mathrm{F}_2^2+2 \mathrm{~F}_1 \mathrm{~F}_2 \cos \theta\)

\(9 \mathrm{~F}^2=\mathrm{F}^2+9 \mathrm{~F}^2+6 \mathrm{~F}^2 \cos \theta\)

\(\cos \theta=-\frac{1}{6}\)

\(\theta=\cos ^{-1}\left(\frac{1}{-6}\right)\)

\(\mathrm{n}=-6\)

\(|\mathrm{n}|=6\)