The driver, Uncle He, filled his car with 30 liters of gasoline at the gas station next to his home (assuming that the car had run out of fuel) and was going to work in a company 160 kilometers away from the gas station. On average, each liter of gasoline can travel 8 kilometers. If he returns on the same road after finishing his work, at least how many liters of gasoline must be added to ensure that he can get home.
司机何叔叔在家旁边的加油站给自己的小车加了30升汽油(假定小车原来油全部用完)后准备到距加油站160千米的某公司办事，平均每升汽油可以行8千米远的路，他办完事后原路返回，至少要再加多少升汽油才能保证到家．
<gadget id="calculator">160 / 8</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<result>10</result>