What is 70g decreased by 20%

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?

How to do this , and can some one explain

Simplify. (-2)^-3 a. -8 b. -1/8 c. 1/8 d. 8