This year the younger brother's age is half of the elder brother's age, and after 9 years, the younger brother's age will be the elder brother's age (4/5). So, how old is brother?
今年弟弟的年龄是哥哥年龄的一半，9年后，弟弟的年龄是哥哥年龄的(4/5)．那么，哥哥今年几岁？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">9 * (4/5)</gadget>
<output>36/5 = around 7.2</output>

<gadget id="calculator">9 - (36/5)</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">2 * (4/5)</gadget>
<output>8/5 = around 1.6</output>

<gadget id="calculator">(8/5) - 1</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<result>6</result>