Hi Jamal. Given the information we have, we know that after having parked for half an hour, the student will have $8 remaining ($9 - $1 = $8). Keep this in mind.
The student will then have to pay $1.50 for each additional hour that he or she remains parked in this lot. So we can then ask this question:
How many times will $1.50 go into $8 without exceeding that amount? This is solved by dividing 8 by 1.5, and obtaining an answer of 5.33. Knowing that a partial hour is charged the same as a full hour, we have to round this answer down to 5 hours.
We can now add the cost of the first half hour to this amount, and the answer is that for $9 a student can park in this lot for as long as 5.5 hours.