What is a three-letter word used to show division in a word problem.

Rachel reads 1/5 of the pages of a book plus 12 pages on the first day. on the second day, she reads 1/4 of the remaining pages plus 15 pages. on the third day, she reads 1/3 of the remaining pages plus 18 pages. on the fourth day, she reads the remaining 70 pages. how many total pages are in the book?

Can you me find the missing length. i attached an image.

The curved part of the figure is the semicircle what is the best approximation for the area of this figure