There is a pile of earth with a total of 400 square meters. There are two cars, big and small. The big cart pulls 7 square meters at a time, and the small car pulls 4 square meters at a time. After transporting the pile of soil, a total of 70 cars were pulled. So how many times has the cart been pulled?
有一堆土方共400方，有大小两辆汽车，大车一次拉了7方，小车一次拉4方，运完这堆土共拉了70车．那么大车拉了多少次？
<gadget id="calculator">400 - 280</gadget>
<output>120</output>

<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<result>40</result>