Uncle Li’s car currently has about 20 liters of gasoline, and each liter of gasoline can travel 6.4km. Uncle Li is going to drive out to do errands. If the round-trip distance is 192km, how many liters of gasoline will Uncle Li need at least?
李叔叔的车现约有20升汽油，每升汽油可行驶6.4km，李叔叔准备开车外出去办事，如果往返路程为192km，李叔叔至少还需要多少升汽油？
<gadget id="calculator">192 / 6.4</gadget>
<output>30</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<result>10</result>