Answer: The average variable cost of producing a backpack is $15.
The formula for calculating the variable cost per unit using the high/low method is:

where
y₂ :  cost at highest level of activity
y₁ :  cost at lowest level of activity
x₂ :  number of units produced at highest level of activity
x₁ :  number of units produced at lowest level of activity
Substituting the values from the question in the formula we get,


