How in Ruby on Rails can you find out what number this element is from the parent element?

Question

Ruby on Rails

For example, there are links to the Mercedes and Models tables.
So I display the models of this Mercedes through the loop:

<% Mercedes.each do |m| %>
<% p m.models.name # Как здесь узнать какой по числу это модель
<% end %>

Here, when outputting, how can you find out what the number of element is,

Answer 1

I guess it will be something like:
p a.index(m.models.name)for an array and
p a.key(m.models.name)for a hash

Answer 2

each_with_index do |item, index|
Or |index,item| I do not remember