Now Zhang Jie is 24 years younger than her mother. Four years later, her mother will be three times as old as Zhang Jie. How old is Zhang Jie this year?
现在张洁比妈妈小24岁，4年以后妈妈的年龄是张洁的3倍，今年张洁多少岁．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<result>8</result>