The radioactive decay of radon-222 can be modeled by the function (a = ce{-0.1813t}) where (a) is the amount remaining, (c) is the original amount, and (t) is the number of days.
a) (c = a₀ e{0.1813t₀})
b) (c = a e{0.1813t})
c) (c = ae{-0.1813t₀})
d) (c = a₀ e{-0.1813t})