Answer: it will take 3.4 days to finish the book.
Explanation:
Let x represent the number of days that it will take sal to finish reading the book.
Sals book has a total number of 52 pages.
Sal already read 18 pages. This means that the number of pages left for Sal to read would be
52 - 18 = 34
He plans to read 10 pages each day until he finishes the book. This means that the number of days it will take Sal to finish the book would be
10x = 34
x = 34/10 = 3.4