The fruit supermarket originally had 310 boxes of apples. A total of 120 boxes were sold in the first four days of last week, and as many boxes were sold in the last three days as in the first four days. How many boxes are left after selling for a week?
水果超市原来有苹果310箱．上星期前四天一共卖掉120箱，后三天卖掉的和前四天同样多．卖了一个星期还剩多少箱？
<gadget id="calculator">120 * 2</gadget>
<output>240</output>

<gadget id="calculator">310 - 240</gadget>
<output>70</output>

<result>70</result>