Answer:
The number of customer per day is 10.
Step-by-step explanation:
Given : I need to increase the number of customers by 20% daily, I talk to an average of 8 customers per hour during an 8 hour shift.
To find : How many customers per day?
Solution :
We have an average of 8 customers.
Increase the number of customers by 20% daily.
i.e. increased number will be 20% of 8,

i.e. 1.60 customer per hour during an 8 hour shift.
So, 
Approximately the number of customer per day is 10.