Zhang Hua reads a story book. He read the whole book (2/5) in the first week, and the rest (11/21) in the second week. There are 90 pages left. How many pages does this storybook have?
张华看一本故事书，第一周看了全书的(2/5)，第二周看了余下的(11/21)，还剩90页．求这本故事书共有多少页？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">11 / 21</gadget>
<output>11/21 = around 0.52381</output>

<gadget id="calculator">(3/5) * (11/21)</gadget>
<output>11/35 = around 0.314286</output>

<gadget id="calculator">1 - (2/5) - (11/35)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">90 / (2/7)</gadget>
<output>315</output>

<result>315</result>