The (1/2) of a number is 4 less than its (3/5), find this number.
一个数的(1/2)比它的(3/5)少4，求这个数．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(3/5) - (1/2)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">4 / (1/10)</gadget>
<output>40</output>

<result>40</result>