Aunt Wang bought 4.5 kilograms of tomatoes in the supermarket, gave the salesperson 10 yuan, and got back 1.9 yuan. How much is a tomato per kilogram?
王阿姨在超市买了4.5千克西红柿，交给售货员10元，找回1.9元．西红柿每千克多少元？
<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>