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.