Question

Laila read 36 pages in 4 hours. Which expression can be used to find the number of pages she read per hour?

Answer 1

Lets see do 36/4 and you should have your answer

Answer 2

36/4 would find the average number of pages she read per hour. since you are dividing the total number by the number of hours she took in total. 
HOWEVER, bare in mind that this is not always an accurate representation of how many pages she DID read, since she might have read some pages slower than others. 
BUT you can generalise and say she read 9 pages (36/4) every hour, on average <span />