There were originally 30 passengers on a bus. After arriving at Station A, 12 passengers got on after going down. At this time, there were exactly 20 passengers on the bus. How many passengers got off at Station A?
一辆公交车上原有30名乘客，到甲站后，下去了一些又上来12名，这时车上正好有20名．在甲站下去了几名乘客？
<gadget id="calculator">12 - 20</gadget>
<output>-8</output>

<gadget id="calculator">30 + (-8)</gadget>
<output>22</output>

<result>22</result>