Mr. Li bought 2 kilograms of apples, paid 15 yuan, and got back 1.8 yuan. How much did he spend on the apples?
李老师买2千克苹果，付出15元，找回1.8元，买苹果花了多少钱？
<gadget id="calculator">15 - 1.8</gadget>
<output>13.2</output>

<result>13.2</result>