Teacher Li from Yuwang Central Elementary School went to the vegetable market and bought 4.5 kilograms of beans. After giving 10 yuan to the salesperson, he got back 1.9 yuan. How much is a kilogram of beans?
预旺中心小学的李老师到菜市场买了4.5千克的豆角，交给售货员10元钱后，找回1.9元，每千克豆角多少钱？
<gadget id="calculator">10 - 1.9</gadget>
<output>8.1</output>

<gadget id="calculator">8.1 / 4.5</gadget>
<output>1.8</output>

<result>1.8</result>