Teacher Wang bought 4.5 kilograms of beans in the supermarket, paid the salesperson 10 yuan, and the salesperson returned 1.9 yuan, how much is it per kilogram of beans?
王老师在超市买4.5千克豆角，付给售货员10元，售货员找回1.9元，每千克豆角多少元？
<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>