There were 18 passengers on the bus, 5 people got off at the district government station, and 7 people got on the bus. How many passengers are there on the bus?
公交车上原有乘客18人，到区府站下车5人，上车7人，车上现有乘客多少人．
<gadget id="calculator">18 - 5</gadget>
<output>13</output>

<gadget id="calculator">13 + 7</gadget>
<output>20</output>

<result>20</result>