Three years ago, the age of the father was three times that of the son. The father is 45 years old this year. How old is the son this year?
三年前爸爸的年龄是儿子的3倍，爸爸今年45岁，儿子今年多少岁．
<gadget id="calculator">45 - 3</gadget>
<output>42</output>

<gadget id="calculator">42 / 3</gadget>
<output>14</output>

<gadget id="calculator">14 + 3</gadget>
<output>17</output>

<result>17</result>