I basically need to find how to solve a ratio chart with a missing value

Question

I have a problem that requires me solving a ratio chart with a missing value. I am really confused but here's the problem:

 

The chart is for a small photo book. Number of pages and total cost. One book has 10 pages and costs $15 Another small book has 18 pages and costs $27. If one book causes $36 how many pages are in it?

Answer 1

p represents the number of pages

10 : 15 :: p : 36

15p = (10)(36)

 

Can you solve for p?

 

Or 

 

Note that for the two given books the cost of each page is $1.50.

1.50p = 36

 

Can you solve for p?