Exercise 20: Defining Commands with an Optional Argument (Solution)
This is the solution to Exercise 20.
\documentclass[11pt]{scrartcl}
\newcommand*{\cost}[2][excl VAT @ 17.5\%]{\pounds#2 #1}
\begin{document}
Example 1 : \cost{50}
Example 2 : \cost{100}
Example 3 : \cost[inc VAT]{25}
Example 4 : \cost[]{75.60}
\end{document}