Show the order from counting

hi, i’m newbie for rails.
i’d like to order the amount of customers after counting in the table.
example
manager#1 has/have 3 customer(s)
customers 1:a
customers 2:b
customers 3:c
manager#2 has/have 1 customer(s)
customers 1:d

i think i should code the order of customers per manager in view
<% for i in manager.customers.size %>

customer : <%= i %>

<% end %>

but it does not work, i have the error.

this time i can display name and the amount of customers for each
manager but i can’t display the order of customers such as customer
no.1,no.2 and so on.

how do i correct that?