Dust mass-loss rate from a massive star given a set of parameters?
Roughly: the mass loss rate for a spherically symmetric wind is given by
$$\dot{M} = 4\pi r^2 \rho v_w,$$
where $\rho$ is the density in the wind, $r$ is the radius at which that density is measured and $v_w$ is the wind velocity.

Here you have $v_w$ and have the mass of material within two concentric radii - so you can work out the average density at some average radius in the shell.

The age of the shell is not relevant to the mass-loss rate, but assuming the wind parameters are unchanged over that time, they do tell you ho much mass has been lost in total $\simeq \dot{M} \tau$.