Sales variance.

Dear john,

How are you?
I hope you are doing well,
Could you help me according to question number 192 which is mentioned in Kaplan Exam kit it says ,
Jones, monthly absorption costing variance analysis report includes a sales mix variance, which indicates the effect on profit of actual sales mix differing from the budget sales mix. the following data are available
Product X product Y
Selling price $12 $11
Less Variable costs $6 $2
Fixed costs $2 $3
Contribution $4 $6
July sales in units
Budget 3000 6000
Actual 2000 8000
Which one of the following best gives the favorable sales mix variance i july.
A. $8000
B. $5333
C. $4000
D. $2667
According to Kaplan the answer is $2667.
According to my answer is $4000.
Actually sir, I had checked the answer mentioned back in kaplan but I found that it took into account the amount of fixed cost into calculation of sales mix variance In other words I mean that I multiplied the difference in units by Standard contribution margin but according to kaplan it used Standard profit per unit.
I know that the company uses Absorption costing techniques but According to my understanding That Fixed Overhead is separated variance.
Could you clarify when we should use Standard Contribution Margin and when we should use Standard profit I do not speak just about Sales mix variance but about sales variance overall.