Notice how much it is for each additional hour:
$5.50. (9.00 – 3.50, 14.50 – 9.00, 20.00 – 14.50)

Let’s substitute in 5.50 into each equation and see if it makes the equation true.
(1) 9.00 + 3(5.50) = 20.00  that one is NOT true because 9 + 16.50 = 25.50 does NOT = 20
(2) 9.00 + 3.50(5.50) = 20  also not true
(3) 2 (5.50) + 9 = 11 + 9 = 20 🙂
(4) 2 (5.50) + 9 does not equal 14.50.

That’s it — 2 more points!
(albeit very cheap parking rates)