Write an exponential function that models the decay of this material.
The function is described by the half-life equation which is expressed as:
An = Ao e^-kt where An is the amount left after t time, Ao is the initial amount and k is a constant.
Find how much radioactive material remains after 18 hours. Round your answer to the nearest thousandth.
1/2Ao = Ao e^-k(78)
k = 8.89 x 10^-3
An = 790e^-8.89 x 10^-3(18)
An = 673.22 kg
