The first step is to complete the diagram as shown below
From the information given,
mass of bonnet = 12kg
Weight = mass x acceleration due to gravity
Thus,
Weight of bonnet = 12 x 9.8 = 117.6 N
Thus, the force acting downwards is 117.6 N
Recall, moment = force x distance from pivot perpendicular to the line of action of the force
The distance from pivot perpendicular to the line of action of the force is PB. We would find PB by applying the cosine trigonometric ratio which is expressed as
Cosθ = adjacent side/hypotenuse
Considering triangle GBP,
hypotenuse = 1
adjacent side = BP
Cos30 = BP/1
BP = 1Cos30 = 0.866
Thus,
Moment = 117.6 x 0.866 = 101.845 Nm
The unknown force, F is perpendicular to the pivot and it is 2m from the pivot. The moment created by this force is 2 * F = 2F
Since the bonnet is in equilibrium(Since the mass acts at the center), it means that
2F = 101.845
F = 101.845/2
F = 51 N