Three pieces of wood having 3.75 cm x 3.75 cm square cross-sections are glued together and to the foundation. If the horizontal force P = 600 kg is applie3d to the central piece, the average shearing stress in each of the glued joints would be
A.20 kg/cm2
B.40 kg/cm2
C.80 kg/cm2
D.430 kg/cm2
E.860 kg/cm2