There are 15 trucks in the parking lot, the number of buses is three times that of trucks, and the number of cars driving 7 is the same as that of buses. How many cars are there?
停车场有15辆卡车，大客车的辆数是卡车的3倍，小汽车开走7辆就与大客车同样多．小汽车有多少辆？
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<gadget id="calculator">45 + 7</gadget>
<output>52</output>

<result>52</result>