A piece is (7/9) meters long, if (4/9) meters are used up, how many meters are left?
一块长(7/9)米，用去(4/9)米，还剩多少米．
<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

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

<gadget id="calculator">(7/9) - (4/9)</gadget>
<output>1/3 = around 0.333333</output>

<result>1/3 = around 0.333333</result>