Xiaoming's mother bought 2.5 kilograms of bananas in the fruit shop. She paid the salesperson 10 yuan and got back 2.10 yuan. How much is a kilogram of bananas?
小明妈妈在水果店里买了2.5千克香蕉，她付给营业员10元钱，找回2.10元钱，每千克香蕉多少元钱？
<gadget id="calculator">10 - 2.1</gadget>
<output>7.9</output>

<gadget id="calculator">7.9 / 2.5</gadget>
<output>3.16</output>

<result>3.16</result>