Answer
$4.4K\frac{N}{m}$
Work Step by Step
We know that
$\tau=rF$
$\implies F=\frac{\tau}{r}$
We plug in the known values as
$F=\frac{81}{(0.38)sin22^{\circ}}$
$F=570N$
Now we can find the force constant as
$K=\frac{F}{x}$
We plug in the known values to obtain:
$K=\frac{570}{0.44-0.31}=4400\frac{N}{m}=4.4K\frac{N}{m}$
