Answer: The phrase is "The time it takes to read a book depends on the number of pages in the book"
so the time is the dependent variable and the pages are the independent variable.
Then you will have a function of the form Time(pages) in which you introduce a number of pages (the total number of pages in a book, in this case) and returns the time it takes to read them all. So the correct answer is A.
Well, your ratio given is 18 to 4. so multiply both numbers (18 and 4) by some number and you will have an equivalent ratio. example: if you had 2 times as many people, then an equivalent ratio would be 18*2 to 4*2 = 36 to 8