Solution:
we are given that
Emma has 15 cookies and eats 2 cookies per day.
So the number of cookies left after n days can be written as

Evan has 45 cookies and eats 8 each day.
So the number of cookies left after n days can be written as

Number of days after which they will have equal number of cookies can be found as below




Hence both will have equal number of cookies after 5 days.