6. A carbon steel ball (E=30x10$^6$ psi, v=0.29) with a radius of 3-in is pressed together with
an aluminum ball (E=10.4x10$^6$ psi, v=0.33) with a radius of 6-in. Determine the
following:
A) The maximum value for the force F if the maximum pressure, $p_o$, is limited to 60 ksi.
B) The contact length, a, due to that force.
C) The maximum shear stress.