For each of the cumulative distribution functions listed below, find the associated PDFs. For each CDF, calculate \(P(x \leq 6)\).

a. \(F(b)=\left(1-\mathrm{e}^{-b / 6}ight) I_{(0, \infty)}(b)\)

b. \(F(b)=(5 / 3)\left(.6-.6^{\operatorname{trunc}(b)+1}ight) I_{\{0, \infty\}}(b)\)