Subtract a number from the difference between (8/9) and (7/12) to get (1/18), find this number.
(8/9)与(7/12)的差减去一个数得(1/18)，求这个数．
<gadget id="calculator">8 / 9</gadget>
<output>8/9 = around 0.888889</output>

<gadget id="calculator">7 / 12</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">(8/9) - (7/12) - (1/18)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>