The two brothers have a total of 100 yuan. The school proposes to donate to poor students. The elder brother donates his own money (4/9), and the younger brother donates his own money (2/7). The two left a total of 60 yuan. It turns out how much money my brother has.
兄弟二人共有100元钱，学校倡议向贫困学生捐款，哥哥捐了自己钱数的(4/9)，弟弟捐了自己钱数的(2/7)，两人一共剩下60元．原来哥哥有多少元．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">100 * (2/7)</gadget>
<output>200/7 = around 28.571429</output>

<gadget id="calculator">100 - (200/7) - 60</gadget>
<output>80/7 = around 11.428571</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">(4/9) - (2/7)</gadget>
<output>10/63 = around 0.15873</output>

<gadget id="calculator">(80/7) / (10/63)</gadget>
<output>72</output>

<result>72</result>