When a car arrives at a certain station, 7 passengers get off and 13 get on, so there are 42 passengers on the car. How many passengers are on the bus before this stop?
一辆汽车到某一站时，有7名乘客下车，13名上车，这时车上有42名乘客．到此站前车上有多少名乘客？
<gadget id="calculator">42 - 13</gadget>
<output>29</output>

<gadget id="calculator">29 + 7</gadget>
<output>36</output>

<result>36</result>