After a 30% discount on a top, the price is 210 yuan. How much cheaper is the current price than the original price?
一件上衣打七折后，售价是210元，现价比原价便宜多少元？
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">210 / (7/10)</gadget>
<output>300</output>

<gadget id="calculator">300 - 210</gadget>
<output>90</output>

<result>90</result>