Help me plz!!!!
The half-life of a radioactive substance is 31.7 years.
(a) Find the exponential decay model for this substance
(b) How long will it take a sample of 400 grams to decay to 300 grams?
(c) How much of the sample of 400 grams will remain after 20 years?
A(t)=A0 e________ Round to the nearest thousandth