The bus company has newly opened a special line from A to B. The whole journey time of this special line is 55 minutes. After arriving at the terminus, rest for at least 15 minutes before the bus turns around again. If there is a bus on both sides of this line A and B every 7 minutes (not necessarily at the same time), how many buses are needed for this line at least?
公交公司新开通了一条从甲地到乙地的专线，该专线全程行驶时间为55分钟，到达总站后，至少休息15分钟，公交车再掉头行驶．如果这条线路甲、乙两边每隔7分钟(不必同一时刻)都发一趟车，则这条线路至少需要多少辆公交车？
<gadget id="calculator">55 + 15</gadget>
<output>70</output>

<gadget id="calculator">70 / 7</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<result>20</result>