More than a dozen trucks transport 315 barrels of gasoline, and each truck transports the same number of barrels, and they are all transported at one time, so how many barrels each truck transports.
十几辆卡车运送315桶汽油，每辆卡车运的桶数一样多，且一次运完，那么每辆卡车运多少桶．
<result>21</result>