A steel bar and an aluminum bar are bonded together as shown to form a composite beam. Knowing that the vertical shear in the beam is 4 kips and that the modulus of elasticity is 29 X 106 psi for the steel and 10.6 X 106 psi for the aluminum, determine
(a) the average shearing stress at the bonded surface,
(b) the maximum shearing stress in the beam.