In a subtraction formula, the sum of the minuend, the subtrahend and the difference is 180, and the ratio of the difference to the subtrahend is 5:4. What is the subtrahend?
在一道减法算式中，被减数、减数与差的和是180，差与减数的比是5：4，减数是多少．
<gadget id="calculator">180 / 2</gadget>
<output>90</output>

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

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

<gadget id="calculator">90 * (4/9)</gadget>
<output>40</output>

<result>40</result>