G represent the page of the book that Grayson is on at the end of t days
C represents the page of the book that Claire is on at the end of t days
So, at the beginning of the month;
Grayson was on page 40
Claire was on page 19
During the month :
Grayson will read 7 pages per day
Claire will read 14 pages per day
When t represents the number of days, So:
G = 40 + 7 t
C = 19 + 14 t
When Grayson and Claire will be on the same page, G will be equal to C
So,
G = C
So,
40 + 7t = 19 + 14 t
Solve to find t
Combine like terms
-14 t + 7t = 19 - 40
-7 t = -21
Divide both sides by -7
t = -21/-7 = 3
So, after 3 days they will be on the same page of the book.