Xiao Fang reads a story book, and has read 42 pages, which is 9 pages less than the rest. How many pages are left in this book?
小方读一本故事书，已经读了42页，比剩下的少9页．这本书还剩下多少页？
<gadget id="calculator">42 + 9</gadget>
<output>51</output>

<result>51</result>