How to get the simple interest

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?

The function show two sisters' savings account and the rate at which they plan to deposit money

Solve each quadratic equation by factoring and using the zero product property. x^2 + 18x = 9x