Input Validation: Regular Expression

a$.$ What is the regular expression pattern to check if an IP address is within the range $192\mathrm{.}168\mathrm{.}1\mathrm{.}0$ to $192\mathrm{.}168\mathrm{.}1\mathrm{.}255?$

b$.$ Write a pattern that can match an Purchase Order Number PO$-$kean$-$yyyy or PO#kean$-$xxxx or PO kean$-$yyyy in a sale, where $x$ is a number from $0$ to $9$ and $y$ is a letter from $A$ to $Z$ or a to $z.$