Use the half-life information to complete each table. (The formula $\mathcal{N}=\mathcal{N}_{0} e^{k t}$ is not required.)
(a) Polonium-210: half-life $=138.4$ days
$$\begin{array}{lllll}\hline t \text { (years) } & 0 & 138.4 & 276.8 & 415.2 \\\mathcal{N} \text { (grams) } & 0.4 & & & 0.025 \\\hline\end{array}$$
(b) Polonium-214: half-life $=1.63 \times 10^{-4}$ second
$$\begin{array}{lllll}\hline t \text { (seconds) } & 0 & & & 6.52 \times 10^{-4} \\\mathcal{N} \text { (grams) } & 0.1 & 0.05 & 0.025 & 0.0125 & \\\hline\end{array}$$