The age of the father is 8 times of Xiao Ming's age, the age of the mother is 7.2 times of Xiao Ming's age, the father is 4 years older than the mother, how old is Xiao Ming this year?
父亲的年龄是小明年龄的8倍，母亲的年龄是小明年龄的7.2倍，父亲比母亲大4岁，小明今年多少岁？
<gadget id="calculator">8 - 7.2</gadget>
<output>0.8</output>

<gadget id="calculator">4 / 0.8</gadget>
<output>5</output>

<result>5</result>