A piece of clothing is priced at 180 yuan after a 10% discount. How much is the price reduction for this piece of clothing?
一件衣服打九折后售价180元，这件衣服降价多少元？
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">180 / (9/10)</gadget>
<output>200</output>

<gadget id="calculator">200 - 180</gadget>
<output>20</output>

<result>20</result>