Answer:
Let's say that the whole book have 5a pages.
First day: a + 12
Second day: (4a)1/4+15= a + 15
Third day: (1/3)[ 4a - (a+15)] +18= a + 13
Forth day: 70
So we get this:
(a + 12) + (a + 15) + (a + 13) + 70 = 5a
a + 12 + a + 15 + a + 13 + 70 = 5a
3a + 110 = 5a
3a - 5a = -110
-2a = -110
a = 55
5a = 5(55) = 275
So the total pages are in the book is:
275 pages