Grandpa is 72 years old this year, father's age is grandpa's (7/9), son's age is father's (3/8), how old is son this year?
爷爷今年72岁，爸爸的年龄是爷爷的(7/9)，儿子的年龄是爸爸的(3/8)，儿子今年多少岁？
<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">72 * (7/9) * (3/8)</gadget>
<output>21</output>

<result>21</result>