Last week, the cafeteria used 3.1 tons of coal in the first 3 days, and an average of 0.8 tons of coal per day in the next 4 days. How many tons of coal did the cafeteria burn on average every day last week?
上个星期食堂用煤，前3天烧煤3.1吨，后4天平均每天烧煤0.8吨．上个星期食堂平均每天烧煤多少吨？
<gadget id="calculator">0.8 * 4</gadget>
<output>3.2</output>

<gadget id="calculator">3.1 + 3.2</gadget>
<output>6.3</output>

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

<gadget id="calculator">6.3 / 7</gadget>
<output>0.9</output>

<result>0.9</result>