Zhang Hua read a storybook. In the first week, he read 90 pages, which is exactly 30% of the storybook. How many pages are left?
章华看一本故事书，第一周看了90页，正好是这本故事书的30%，还剩多少页没看？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">90 / (3/10)</gadget>
<output>300</output>

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

<result>210</result>