Representation of data — practice question

The diagram gives the cross-section $OABCDE$ passing through the centre of mass of a uniform prism. The interior angles of the cross-section at $O$, $A$, $C$, $D$ and $E$ are each right angles. $OA = 0.4\,\mathrm{m}$, $AB = 0.5\,\mathrm{m}$ and $BC = CD = 1\,\mathrm{m}$. The prism has weight $120\,\mathrm{N}$. A force of magnitude $F\,\mathrm{N}$ acting along $DE$ keeps the prism in equilibrium while $OA$ lies on a rough horizontal surface.