Cars A and B jointly undertake the task of transporting 163 tons of cement. Car B arrives only after car A transports 28 tons alone. If car A transports 12 tons per hour and car B transports 15 tons per hour, how many hours will it take for the two cars to cooperate to complete the task?
甲乙两车共同担负运送163吨水泥的任务．甲车单独运送28吨后乙车才赶来，如果甲车每小时运送12吨，乙车每小时运送15吨，两车还要合作几小时才能完成了任务？
<gadget id="calculator">163 - 28</gadget>
<output>135</output>

<gadget id="calculator">12 + 15</gadget>
<output>27</output>

<gadget id="calculator">135 / 27</gadget>
<output>5</output>

<result>5</result>