Xiao Ming bought 30 apples and ate 12 in 3 days, how many are left? What is the correct column
小明家买了30个苹果，3天吃了12个，还剩多少个？正确的列式是多少
<gadget id="calculator">30 - 12</gadget>
<output>18</output>

<result>18</result>