The sum of minuend, subtrahend and difference is 180, the ratio of subtrahend and difference is 4:5, what is the difference.
被减数、减数、差的和是180，减数与差的比是4：5，差是多少．
<gadget id="calculator">180 / 2</gadget>
<output>90</output>

<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">90 * (5/9)</gadget>
<output>50</output>

<result>50</result>