Answer:
The total contribution margin for the month under variable costing is $161,640.
Explanation:
Contribution: The contribution shows a difference between the sales and variable cost.
So, Contribution = Sales per unit - Variable cost per unit
Variable costing : Under variable costing, the cost which is change when production level changes than it is known as variable costing.
The examples of variable costing is direct material, direct labor, variable manufacturing overhead, etc.
Computation of the total contribution margin for the month under variable costing is shown below :
First we have to calculate contribution margin . The calculation is computed below:
= Selling price - direct material - direct labor  - Variable manufacturing overhead - Variable selling and administrative expense
= $112 - $21 - $45 -$6 - $4
= $36
Hence, the contribution margin is $36.
Now, the total contribution margin = Unit sold × contribution margin
                             = 4,490 × $36
                             = $161,640
Hence, the total contribution margin for the month under variable costing is $161,640.