Answer:
40.5 sec
Explanation:
The flow rate is (12 ft) / (9 sec), or 4/3 ft/ sec.
In 54 sec, the water will have moved 
(4/3 ft/sec)(54 sec) = 72 ft.
If the flow rate is 4/3 ft/sec and the distance covered is 54 ft, we divide 
54 ft by (4/3 ft/sec) to determine how long it takes the water to flow 54 ft:
 54 ft
---------------- = 40.5 sec
(4/3 ft/sec)