问题标题：
英文的数学题,请将每一步用英文解释清楚thetotalcosttouseanin-flightphoneononeairlineincludesa$3.99connectionfeeplues$3.99perminute.a,writeafunctionruleforthecostofacallusinganin-flightphone.b,findthe
问题描述：
英文的数学题,请将每一步用英文解释清楚
thetotalcosttouseanin-flightphoneononeairlineincludesa$3.99connectionfeeplues$3.99perminute.
a,writeafunctionruleforthecostofacallusinganin-flightphone.
b,findthecostofa10-minutein-flightcall.
顾雪峰回答：
a,thecostofacallincludesa3.99dollarconnectionfeeplues3.99dollarperminute,sothefunctionruleforthecostofacallisy=3.99+3.99x(dollar)b.a10-minutein-flightcallcosty=3.99+3.99*10=43.89（dollar）
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