A person has to take the light rail or bus every morning to work and to leave work in the afternoon without changing trains on the way. In 19 days, this person took the light rail 11 times and took the bus 15 times in the morning. Then, how many times did he take the bus in the afternoon?
某人每天早上上班和下午下班都要乘轻轨或公共汽车，途中不换乘．在19天中这个人乘轻轨共11次，在早晨乘公共汽车共15次，那么，在下午乘公共汽车共多少次．
<gadget id="calculator">19 * 2</gadget>
<output>38</output>

<gadget id="calculator">38 - 11 - 15</gadget>
<output>12</output>

<result>12</result>