$4\mathrm{.}27$ An open$-$ended, thin$-$walled cylinder, $r=25cm$ and $t=0\mathrm{.}25cm$ is acted on by an internal pressure $p$ and an axial force $F.$ Find the values of $p$ and $F$ acting in each of the following two situations:

$($a$){}_m=100M\frac{N}{m^2}$

${}_n=30M\frac{N}{m^2}$

${}_{mn}=$

$($b$){}_m=100M\frac{N}{m^2}$

${}_n=100M\frac{N}{m^2}$

${}_{mn}=?$