Buy a barrel of oil, the weight of the barrel is 8 kilograms, and the payment is 37.1 yuan. After half of the barrel is used, the weight of the barrel is 4.5 kilograms. How much is the oil per kilogram?
买一桶油，连桶重8千克，付款37.1元，用去一半后连桶重4.5千克，每千克油多少元？
<gadget id="calculator">8 - 4.5</gadget>
<output>3.5</output>

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

<gadget id="calculator">37.1 / 7</gadget>
<output>5.3</output>

<result>5.3</result>