Answer:

Where, a =additional tickets per day sold by Sam. (must be less than 8)
Explanation:
Let after x days, Sam and Tony have sold the same amount of tickets
Given,
For Sam,
The fixed number of tickets sold = 20,
Let additional tickets per day = a,
So, the total tickets after x days = fixed ticket + additional tickets for x days
= 20 + ax
For Tony,
The fixed number of tickets sold = 5,
Additional tickets per day = 8,
So, the total tickets after x days= 5+ 8x,
Thus, we can write,
20 + ax = 5 + 8x
20 - 5 = 8x - ax
15 = (8-a)x

Hence, after
days they would have same amount of tickets.