A shear spring is made from two blocks of rubber, each having a height h, width b, and thickness a. The blocks are bonded to three plates as shown. If the plates are rigid and the shear modulus of the rubber is G, determine the displacement of plate A if a vertical load P is applied to this plate. Assume that the displacement is small so that $\delta $=a tan$\gamma $ $\approx $ a $\gamma $. <image 1>
['Pa/(2bhG)', 'Pa/(bhG)', 'Pab/(2hG)', '2Pa/(bhG)']