An isotope of Sodium, $^{24}$Na, has a half-life of $15$ hours. A sample of this isotope has mass $2$ g.

(a) Find the amount remaining after $60$ hours.
(b) Find the amount remaining after $t$ hours.
(c) Estimate the amount remaining after $4$ days (to the nearest thousandth).
(d) Estimate the time (to the nearest tenth) required for the mass to be reduced to $.01$ g by graphing the function.

(a) g
(b) g
(c) g
(d) hours