The driver, Uncle Wang, fills up 30 liters of fuel at the gas station, and then goes to work at a company 280 kilometers away from the gas station. Calculated on the basis that each liter of gasoline can travel 8 kilometers, how many liters of gasoline do he need to refill when he returns?
司机王叔叔在加油站加了30升油后，去距离加油站280千米的公司去办事，按每升汽油可行驶8千米计算，回来还需要加多少升汽油？
<gadget id="calculator">280 * 2</gadget>
<output>560</output>

<gadget id="calculator">560 / 8</gadget>
<output>70</output>

<gadget id="calculator">70 - 30</gadget>
<output>40</output>

<result>40</result>