英语数学问题。看不懂啊。

A utility company measures gas consumption by the hundred cubic feet, CCF.The company has a three-step rate schedule for gas customers.First, there is a minimum charge of $5.00 per month for up to 3 CCF of gas used.Then,for the next 6 CCF,the charge is $0.75 per CCF.Finally,after 9 CCF,the charge is $0.55 per CCF.Represent the cost of g CCF of gas if g is greater than 9.

谁帮忙做下。头大。

5+6*0.75+(g-9)*0.55=0.55g-4.45

(g>9CCF)

最低消费是每月5美元，在未达到 3 CCF 时

大于3未达到9CCF 时，超出数每月增加0.75美元

超过9 CCF 时超出数每月增加0.55美元

cost=5+6*0.75+(g-9)*0.55=0.55g-4.45