Understand the geometry and given parameters.

Step 1: Understand the geometry and given parameters.
The derrick crane has the following members and properties:

• Load $F = 30 \text{ kN}$ acting vertically downwards at C.
• Support $AB = 4 \text{ m}$. AB is vertical.
• Struts $EB = DB = 4.6 \text{ m}$. E, B, D, G are in the horizontal plane.
• Point B is supported on horizontal rollers, meaning the reaction at B is purely vertical.
• Crane arm BC forms an angle of $60^\circ$ with the horizontal line BG. This means $\angle CBG = 60^\circ$.
• Angle $ABC = 120^\circ$.