Two blocks of rubber with a modulus of rigidity G =10 MPa are bonded to rigid supports and to a plate AB. Knowing that b = 200 mm and c = 125 mm, determine the largest allowable load P and the smallest allowable thickness a of the blocks if the shearing stress in the rubber is not to exceed 1.2 MPa and the deflection of the plate is to be at least 6 mm.