Xiaohong’s family has a barrel of oil that weighs 8 kilograms. After half of it is used up, the barrel still weighs 4.5 kilograms. How much is the original oil?
小红家有一桶油连桶重8千克，用去一半后，连桶还重4.5千克，原有油多少千克？
<gadget id="calculator">8 - 4.5</gadget>
<output>3.5</output>

<gadget id="calculator">3.5 * 2</gadget>
<output>7</output>

<result>7</result>