The half-life of strontium-90 is 28 years. Suppose we have a 48 mg sample.

(a) Find a function that models the mass $m(t)$ remaining after $t$ years.
$m(t) =$

(b) How much of the sample will remain after 80 years?
$m(80) =$ mg.

(c) How long will it take the sample to decay to a mass of 12 mg?
Your answer is years.

Note: if you round off values in earlier parts of this problem, the answers might be marked as correct. But, the error from rounding off can be magnified in later parts of the problem and lead to answers which are not close enough to being marked correct. It is a good idea to not use rounded values when computing later parts of a problem.