creating a free body diagram will assist you in solving the problem
First thing we need to do is sum the forces in the y direction. (given: FAy = FBy)
ΣFy = 0 = -1800N/m(a) – (600N/m) (4-a) + 2(FAy)
When the forces in the y direction are summed we have 2 unknowns (a, FAy) so we will need a second equation. Let’s sum the moments about point A.
ΣMA= 0 = 1800N/m(a)(2/3)(a) + (600N/m)(4-a)(2/3)(4+a) – 4m(FBy)
Now we have two equations and two unknowns. Solve the system of equations.
Solving these two equations will output two possible answers,
1. a = 1m, FAy = FBy = 1800 N
2. a = 2m, FAy = FBy = 2400 N