There are some passengers on the bus when it leaves the starting station. At station A, get off half of the passengers, and then get on the bus with 7 people; at station B, only 9 people get on the bus, and there are 30 passengers on the bus at this time. How many people were in the car when it drove from the starting station?
一辆公共汽车从起点站开出时车上有一些乘客．到了A站，先下车一半人数，再上车7人；到了B站，只是上车9人，这时车上共有乘客30人．这辆车从起点站开出时车上有多少人？
<gadget id="calculator">30 - 9 - 7</gadget>
<output>14</output>

<gadget id="calculator">14 * 2</gadget>
<output>28</output>

<result>28</result>