Mohammad 先生乘出租车从家去办公室。
他的出租车车费是根据以下收费标准计算的：

首 1 公里或以下	$4.30
每后续 400 米或以下	$0.24
每等候 45 秒或以下	$0.24

出租车在红绿灯处停了一次，行驶的总路程为 7 公里到达他的办公室。Mohammad 先生支付了 $9.10。出租车在红绿灯处等候的最长可能时间是多少？ 答：___

1. Calculate the remaining distance after the first kilometre

Remaining distance $= 7\text{ km} - 1\text{ km} = 6\text{ km} = 6000\text{ m}$

2. Calculate the cost of the remaining distance

Number of $400\text{ m}$ blocks $= \frac{6000}{400} = 15$
Cost for remaining distance $= 15 \times \char36{}0.24 = \char36{}3.60$

3. Calculate the amount paid for waiting time

Total cost for distance $= \char36{}4.30 + \char36{}3.60 = \char36{}7.90$
Amount paid for waiting $= \char36{}9.10 - \char36{}7.90 = \char36{}1.20$

4. Calculate the longest possible waiting duration

Number of $45$-second waiting blocks $= \frac{\char36{}1.20}{\char36{}0.24} = 5$
Since the charge is for every $45$ seconds or less, the longest possible duration for $5$ blocks is exactly $5 \times 45\text{ s}$.
Longest duration $= 5 \times 45 = 225\text{ seconds}$