Answer:
10 customers were spoken to in every 30 minutes
Explanation:
First, we convert 40 hours into minutes by multiplying it with 60 [as 1 hour = 60 minutes]
So, 40 hours = 40*60 minutes
= 2400 minutes
In 2400 minutes, number of customers served = 800
In 1 minute, number of customers served =

In 30 minutes, number of customers served =

=

=

=

= 10
So,
10 customers were spoken to in every 30 minutes