From Mechanics

The forces on the particle are in equilibrium as the particle is at rest.

The sum of the forces up the plane (resolving up the plane)

\displaystyle \begin{align} & F-mg\sin {{20}^{\circ }}=0 \\ & \\ & F=mg\sin {{20}^{\circ }}=20\times 9\textrm{.}8\times 0\textrm{.}342=67\textrm{.}0\ \text{N} \\ \end{align}