Aunt Wang bought 5 kg of apples and 2 kg of bananas and paid a total of 30.60 yuan; Aunt Zhang bought the same 5 kg of apples and 4 kg of bananas and paid a total of 40.20 yuan. How much is a banana per kilogram?
王阿姨买5千克苹果和2千克香蕉，共付30.60元；张阿姨买同样的苹果5千克和香蕉4千克，共付40.20元．香蕉每千克多少元．
<gadget id="calculator">40.2 - 30.6</gadget>
<output>9.6</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">9.6 / 2</gadget>
<output>4.8</output>

<result>4.8</result>