Is using WACM the right approach to this question? Are my calculations correct?

1.Ignore any current plans.Using last year's actual data and sales mix, how many total cases would David need to sell in order to earn $80,000 before tax?How many cases of each of the four labels would TM need to produce?

Cost-volume- profit analysis

Weighted Average Contribution Margin = WACM

Aggregate Sales - Aggregate Variable Expenses/# of units sold = WACM

WACM per case = $10.22

Total CM/Total Cases sold = 31,911.41/30,730

Required total cases to sale = 35,227

Required pre-tax Income$80,0000

Direct Fixed Costs$34,633.84

Common Fixed Costs$245,389.44

Req CM$360,023.28

Req CM/WACM per Case=360023.28/10.22