This year, the combined age of Dandan, his father, mother and younger brother is 120 years old. When the father's age is three times Dandan's age, the mother's age is exactly three times the younger brother's age, and the younger brother is 12 years old at that time. So how old is Dandan this year?
今年，丹丹和父亲、母亲、弟弟的年龄和是120岁．当父亲的年龄是丹丹年龄的3倍时，母亲的年龄恰好也是弟弟年龄的3倍，当时弟弟12岁．那么丹丹今年多少岁．
<gadget id="calculator">120 - 48</gadget>
<output>72</output>

<gadget id="calculator">72 / 4</gadget>
<output>18</output>

<result>18</result>