The bus was full when it left the departure station. When arriving at Hubin Station, 25% of the passengers get off the bus, and 21 people get on the bus, and 9 of them have no seats at this time. How many passengers are in the car now?
客车从始发站开出时正好满座．到湖滨站时，有25%的乘客下车，又有21人上车，这时9人没有座位．现在车上有乘客多少人？
<gadget id="calculator">21 - 9</gadget>
<output>12</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">12 / (1/4)</gadget>
<output>48</output>

<gadget id="calculator">48 + 9</gadget>
<output>57</output>

<result>57</result>