When Xiaofang’s father drove from home, there was 30 liters of gasoline in the mailbox. He first delivered the goods to a freight station 180 kilometers away from home, and then returned along the original road. Calculated by the calculation that each liter of gasoline can travel 8 kilometers, there are at least 30 liters of gasoline on the way. How many liters of gasoline can be added?
小芳的爸爸开车从家里出发时邮箱里有30升汽油，他先去离家180千米的货站送货，然后沿原路返回，按每升汽油可行驶8千米计算，途中至少还能加多少升汽油？
<gadget id="calculator">2 / 8</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">180 * (1/4)</gadget>
<output>45</output>

<gadget id="calculator">45 - 30</gadget>
<output>15</output>

<result>15</result>