A rectangular piece of metal (0.3 m by 0.4 m) is hinged () as shown in the upper left corner, hanging so that the long edge is vertical. Force A (20 N) acts to the left at the lower left corner. Force B (10 N) acts down at the lower right corner. Force C (30 N) acts to the right at the upper right corner. (Take counterclockwise to be positive.)
What is the torque of force A about the pivot?