The age of the son this year is the age of the father (3/7). After 15 years, the age of the son is the age of the father (3/5). How old is the son this year?
今年儿子的年龄是父亲年龄的(3/7)，15年后，儿子年龄是父亲年龄的(3/5)，今年儿子几岁？
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">15 * (3/5)</gadget>
<output>9</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<gadget id="calculator">7 / 3</gadget>
<output>7/3 = around 2.333333</output>

<gadget id="calculator">(7/3) * (3/5)</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">(7/5) - 1</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">6 / (2/5)</gadget>
<output>15</output>

<result>15</result>