7. (10 points) Lei Ke bought a new book and liked it very much. On the first day, he read $\frac{1}{5}$ of the book plus 12 pages. On the second day, he read $\frac{1}{4}$ of the remaining pages plus 15 pages. On the third day, he read $\frac{1}{3}$ of the remaining pages plus 18 pages. At this point, there were still 42 pages left to read. So, the total number of pages in the book is $\qquad$ .