There is a pile of soil 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 this pile of soil, a total of 70 cars were pulled. Q: How many times has the cart been pulled?
有一堆土共400方，有大小两辆汽车，大车一次拉7方，小车一次拉4方，运完这堆土共拉了70车．问：大车拉了几次？
<gadget id="calculator">4 * 70</gadget>
<output>280</output>

<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>