Teacher Wang bought 4.5 kilograms of eggs at the supermarket, paid 50 yuan at the cash register, and got back 9.5 yuan. How much is it per kilogram of eggs?
王老师在超市买了4.5千克鸡蛋，在收银台付款50元钱，找回了9.5元，问每千克鸡蛋多少元钱？
<gadget id="calculator">50 - 9.5</gadget>
<output>40.5</output>

<gadget id="calculator">40.5 / 4.5</gadget>
<output>9</output>

<result>9</result>