Xiao Ming buys a watermelon that weighs 7.5 kilograms and costs 2.10 yuan per kilogram. How much does it cost in total?
小明买一个西瓜，重7.5千克，每千克2.10元，一共需要多少钱？
<gadget id="calculator">2.1 * 7.5</gadget>
<output>15.75</output>

<result>15.75</result>