After Uncle Li fills up 15 liters of gasoline at the gas station and goes to a destination 120 kilometers away from the gas station, each liter of gasoline can travel 6 kilometers.
李叔叔在加油站加了15升汽油后，去距离加油站120千米的目的地，每升汽油可行驶6千米，往返至少还需要加多少升汽油？
<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">120 * (1/3)</gadget>
<output>40</output>

<gadget id="calculator">40 - 15</gadget>
<output>25</output>

<result>25</result>