There is a barrel of gasoline, the bus has used half of the barrel of oil, and the car has used the remaining half of the oil. At this time, there are still 30 liters of gasoline in the barrel. How many liters is this barrel of oil originally?
有一桶汽油，大巴车用了这桶油的一半，小轿车用了剩下油的一半，这时桶里还剩30升汽油．这桶油原来一共有多少升？
<gadget id="calculator">30 * 2 * 2</gadget>
<output>120</output>

<result>120</result>