"account for" in this context means :make up a specified amount or proportion of : eg social security accounts for about a third of total public spending.
What is it you don't understand in the last part?
a) what a benefits package is?
b) why 1/1,000 of the cost of this is added in calculating the production cost of each product item?
Are you sure you understand the concept of Attributable Costs?
Student or Learner