Keep Cool Air-Conditioning charges $ 60 for the first 30 minutes of every house call and $ 15 for each additional quarter hour

题目

Keep Cool Air-Conditioning charges $ 60 for the first 30 minutes of every house call and $ 15 for each additional quarter hour. In addition, the customer has to pay for any required parts needed for repairs. If Mrs. Lewis’s bill was $ 225, which included $ 90 for parts, how long did the air-conditioning repair technician work?

选项

1 hour and 15 minutes

1 hour and 45 minutes

2 hours

2 hours and 15 minutes

3 hours

解析

总费用 = 前30分钟费用60 + 每15分钟费用15 + 零件费用设需要的**刻钟数**（15分钟为1刻钟）为 $X$。因此： \[ 225 = 60 + 15X + 90 \] 解得 $X = 5$ 所以，总时长 = 初始30分钟 + $15 \times 5$ 分钟 = 105分钟 = 1小时45分钟答案：选项B

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