Uncle Li went to other places to do business, and the whole journey was 252 kilometers. His car currently has 18 liters of gasoline. If each liter of gasoline can travel 5.6 kilometers, how many liters of gasoline does Uncle Li need to add at least to travel the entire distance?
李叔叔到外地办事，全程共252千米．他的车现有18升汽油，如果每升汽油可行驶5.6千米，李叔叔至少需要加多少升汽油才能行完全程？
<gadget id="calculator">252 / 5.6</gadget>
<output>45</output>

<gadget id="calculator">45 - 18</gadget>
<output>27</output>

<result>27</result>