A$-1\mathrm{.}1$: A hollow circular post ABC $($see figure$)$ supports a load $P_1=16kN$ acting at the top. A second load $P_2$ is uniformly distributed around the cap plate at $B.$ The diameters and thicknesses of the upper and lower parts of the post are $d_{AB}=30mm,t_{AB}=12mm,d_{BC}=60mm,$ and $t_{BC}=9mm,$ respectively. The lower part of the post must have the same compressive stress as the upper part. The required magnitude of the load $P_2$ is approximately:

$($A$)18$ kN

$($B$)22$ kN

$($C$)28$ kN

$($D$)46$ kN