Nico borrows 3 books from the library on Monday.  On Monday, he reads the first book with a total of 20 pages.  On Tuesday, he reads the second book with a total of 12 pages.  On Wednesday, he reads the third book.  If he has read a total of 51 pages from Monday to Wednesday, how many pages did he read on Wednesday?
From Monday to Tuesday, Nico reads a total of 20 + 12 = 
<gadget id="calculator">20+12</gadget>
<output>32</output>
32 pages.
On Wednesday, he read a total of 51 - 32 = 
<gadget id="calculator">51-32</gadget>
<output>19</output>
19 pages.

<result>19</result>