Daniel completed reading a book in 6 days. Each day, he read 4 pages more than
the previous day. Given that he read 36 pages on the 3rd day, find the total number
of pages in the book.
you have an AP with d = 4
so, a+2d = 36, and a = 28
total pages in 6 days is thus
6/2 (2a+5d) = ____