Answer:
Total relevant cost of 21,962 * $0.39 = $8,565.18
making internally
Less: Total relevant 21,962 * 0.22 = $4,831.64
cost of purchasing
Savings in cost $3,733.54
Conclusion: Manufacturing the hard cardboard box internally will save cost of $3,733.54 as compared to cost of purchasing the same quantity of box needed from supplier.
Note: Fixed costs is not relevant cost as it is unavoidable.