Five forces act on a model truss built by a civil engineering student as part of a design...

Five forces act on a model truss built by a civil engineering student as part of a design project. The dimensions are b = 300 mm and h = 400 mm and F = 100 N. The sum of the moments of the forces about the point where Ax and Ay act is zero. If the weight of the truss is negligible, what is the force B?