Answer
$x \leq 7$
You can park for up to 3.5 hours.
Work Step by Step
1 dollar for the first half-hour and .60 dollars for each additional half hour
Let $x$ be the number of half hours after the first half hour
$1*(1)+.6*(x-1)$
$1+.6x-.6$
$.4+.6x$
$.4+.6x \leq4$
$.4+.6x-.4 \leq4-.4$
$.6x \leq 3.6$
$.6x/.6 \leq 3.6/.6$
$x \leq 6$
We need to add the original half hour, so $x \leq 7$
