Answer:
3 (quarters)
Step-by-step explanation:
One could pay for exactly 80 minutes (1 h, 20 min) of parking using 5 nickels (35 min), 1 dime (15 min), and 1 quarter (30 min), for a total of 7 coins.
On the other hand, one could pay for 90 minutes (1 h, 30 min) using 3 quarters.
The minimum number of coins required to purchase 80 minutes of parking time is 3 (quarters).
