Radon- 220 is radioactive, and decays into polonium- 216 . This is a first-order process, just like the radioactive decay of carbon-14, and it has a rate constant of $0.0125 \mathrm{~s}^{-1}$. When the concentration of radon-220 is $1.0 \times 10^{-9} \mathrm{~mol}$ $\mathrm{L}^{-1}$, what is the rate of the reaction?