Help please !?

Consider the crane lifting the load shown. If the maximum crane loading on member A is 40,000 lbs (18,140 kg) as a bending limit, calculate the heaviest load that can be lifted.

The answer is Load = 40,000/(cos 45-cos 80) = 40,000/0.533 = 75.0 klbs but don't understund the equation !
2 answers 2