Li Hua reads a famous book. The ratio of the number of viewed pages to the number of unread pages is 2:5, and the number of unread pages is 180 more than the number of viewed pages. How many pages does this book have?
李华看一本名著．已看页数与未看页数的比为2：5，未看页数比已看页数多180页．这本名著一共有多少页？
<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(5/7) - (2/7)</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">180 / (3/7)</gadget>
<output>420</output>

<result>420</result>