Which of the following sets of vectors spans a plane R^3

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?

Which expression is equivalent to 8(k + m) − 15(2k + 5m)?

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