What's the whole unit?

This task is about fractions of different whole units.
  
Key   
   = 1 full cola bottle =  one 8-pack  = 1 case
   = 1 empty cola bottle
   = one 4-pack

Use the diagram of the two cases below to answer the questions that follow.

The first question has been done for you.

a)
 
How many 4-packs of full cola bottles are there? 6 1/2
(include any fractional part of a 4-pack)
 
  
b)

How many 8-packs of full cola bottles are there? _____
(include any fractional part of an 8-pack)

 
c)

How many cases of full cola bottles are there? _____
(include any fractional part of a case)

 
d)
What fraction of all the bottles are full? _____