Xiao Ming is 15 years old this year, his father is three times his age, how old is his father?
小明今年15岁，爸爸年龄是小明的3倍，爸爸比小明大几岁？
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<gadget id="calculator">45 - 15</gadget>
<output>30</output>

<result>30</result>