Xiao Ming went to the market and bought 3.5 kilograms of potatoes. After giving it to the salesperson for 10 yuan, he got back 1.6 yuan. How much is it per kilogram of potatoes?
小明去市场买了3.5千克的土豆，交给售货员10元后，找回1.6元，每千克土豆多少钱？
<gadget id="calculator">10 - 1.6</gadget>
<output>8.4</output>

<gadget id="calculator">8.4 / 3.5</gadget>
<output>2.4</output>

<result>2.4</result>