AAA Electronics sells two models of tablet computers. The budgeted price per unit for the wire less model is $120 and the budgeted price per unit for the wireless and cellular model is $260. The master budget called for sales of 20,000 wireless models and 5,000 wireless and cellular models during the current year. Actual results showed sales of 15,000 wireless models, with a price of $125 per unit, and 8,000 wireless and cellular models, with a price of $250 per unit. The standard variable cost per unit is $50 for a wireless model and $100 for a wireless and cellular model. 

Required :
a. Compute the activity variance for these data. 

b. Break down the activity variance into mix and quantity parts.