$3\mathrm{.}2.$ Given a rigid pavement $16$ inches thick on a silty clay subgrade with a modulus of subgrade reaction of $200$pci, determine the extreme fiber stress for the interior load case for the following:

a$.$ Single wheel, $50$kips,$100-$ tire pressure.

b$.$ Dual wheels, $50$kips per wheel, $100-$psi tire pressure, wheels spaced $37\mathrm{.}5$ inches $c-c.$

c$.$ Twin$-$tandem wheels, $50$ kips per wheel, $100-$psi tire pressure, duals $37\mathrm{.}5$ inches c$-$c$.,$

tandems $60$ inches $c-c.$

d$.$ Single wheel, $50$ kips, $200-$psi tire pressure.