A parking garage allows users to park the first hour free and then charges \( \$ 2.50 \) for each additional hour or fraction of an hour. Which equation represents this situation?
\(f ( x ) = 2.50 [ x ] \)
\( f ( x ) = 2.50 + [ x ] \)
\( f ( x ) = 2.50 [ x - 1 ] \)
\( f ( x ) = 2.50 [ x + 1 ] \)