Uncle Li’s car has 35 liters of gasoline in the fuel tank, and each liter of gasoline can travel 6.4 kilometers. He has to go to a provincial capital 120 kilometers away for work. How many liters of gasoline do he need to add for a round trip?
李叔叔的汽车油箱内有35升汽油，每升汽油可行驶6.4千米，他要去距离120千米的省城办事，往返一次至少还要加多少升汽油？
<gadget id="calculator">2 / 6.4</gadget>
<output>0.3125</output>

<gadget id="calculator">120 * 0.3125</gadget>
<output>37.5</output>

<gadget id="calculator">37.5 - 35</gadget>
<output>2.5</output>

<result>2.5</result>