Three forces of magnitudes $6 \mathrm{~N}, 6 \mathrm{~N}$, and $\sqrt{72} \mathrm{~N}$ act at corner of cube along three sides as shown in figure. Resultant of these forces is:(a) $12 \mathrm{~N}$ angle $\mathrm{OB}$
(b) $18 \mathrm{~N}$ along $\mathrm{OA}$
(c) $18 \mathrm{~N}$ along $\mathrm{OC}$
(d) $12 \mathrm{~N}$ along $\mathrm{OE}$