Let's consider the following diagram:

For the equilibrium of the system, the net torque, according to the above figure, on the system about point A should be zero.
With reference to the above figure, the net anti-clockwise torque about A is
τa=F2L...(1)
And, the net clockwise torque about the same point is
τc=Wcosθ×2L...(2)
Equations (1) and (2) imply that
Wcosθ×2L=F2L⇒12×10×cos60∘×(2L)=F2L⇒F2=2120×10×cos60∘=30
Hence, the required weight can be expressed as
F2=3kg−wt