The father is 30 years older than the son, and the ratio of the age of the son to the father next year is 1:3, so how old is the son this year?
父亲比儿子大30岁，明年儿子与父亲年龄的比是1：3，那么儿子今年多少岁．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 1</gadget>
<output>14</output>

<result>14</result>