Olivet Devices sells two models of fitness devices. The budgeted price per unit for the wireless model is $$55$ and the budgeted price per unit for the wireless and cellular model is $$100.$ The master budget called for sales of $53,600$ wireless models and $13,400$ wireless and cellular models during the current year. Actual results showed sales of $39,500$ wireless models, with a price of $$52$ per unit, and $17,100$ wireless and cellular models, with a price of $$97$ per unit. The standard variable cost per unit is $$42$ for a wireless model and $$77$ for a wireless and cellular model.

Required:

a$.$ Compute the sales activity variance for these data.

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