On monday, anya read 11 pages of a book in 1/2 hour. on tuesday, she read 18 pages in 3/4 hour. did anya's reading speed increase by more than 10% from monday to tuesday? justify your answer.

The way you should go about solving this really depends on how your teacher taught you...However, here's what I would recommend...
You know that 1/2 an hour is equal to 30 minutes, and 3/4 of an hour is equal to 45 minutes.
Using this you can  then solve for how many pages she read per minute by dividing the number of pages read by the number of minutes read:11 pages/ 30 minutes to give you Monday's reading speed,and18 pages/ 45 minutes to give you Tuesday's reading speed.

Next, to calculate a percentage increase you need to do the following:
1. Determine the difference between the speeds (this means you will subtract Monday's reading speed from Tuesday's reading speed.)
2. Next you take that number and divide it by Monday's reading speed.
3. Multiply that answer by 100 to get the percentage.

I'm not going to tell you the speeds, as you should try to attempt to solve it by yourself, and I'm sure you need to show your work. I will however tell you that you should find there was a 3.3% increase from Monday to Tuesday.

If you need more help, let me know!  

24 is the correct answer.

The shelves will hold 270 books in total