Answer
$81\;lb$.
Work Step by Step
The given values are
$F_l=8100\;lb$
$r_l=30\;in.$
$r_s=3\;in.$
Formula
$\Rightarrow \frac{F_l}{F_s}=\frac{r^2_l}{r^2_s}$
Substitute all the values.
$\Rightarrow \frac{8100\;lb}{F_s}=\frac{(30\;in.)^2}{(3\;in.)^2}$
Simplify.
$\Rightarrow (8100\;lb)\frac{(3\;in.)^2}{(30\;in.)^2}=F_s$
$\Rightarrow F_s=81\;lb$
Hence, the $F_s$ is $81\;lb$.
