Mom bought back 4.5kg of beans at the vegetable market, handed it over to the seller for 10 yuan, and got back 1.9 yuan. How much is beans per kg?
妈妈在菜场买回4.5kg豆角，交给卖家10元后，找回1.9元．豆角每kg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>