if Tim has read 10% of the book, that means he still hasn't read 90% of it yet, and we know that that 90% is 45 pages, so say the book has a total amount of pages of "x", which is 100%.
I would start by saying how much I enjoyed this lesson and how it has helped me in many ways I would also like to state how it was difficult at first but once I started to understand it, it became really easy and would like to thanks the teacher for teaching it.