Edwards and Bell market a single line of home computers, dubbed the XL$-98.$ The master budget for the coming year contained the following items: sales revenue, $$380,000$; variable costs, $$250,500$; fixed costs, $$100,100.$ Actual results for the year were as follows: sales revenue, $$360,000$; variable costs, $$225,100$; fixed costs, $$95,200.$ The flexible$-$budget operating income for the year was $$35,100.$

a$.$ The total master $($static$)$ budget variance in operating profit for the period is $$10,300$ favorable.

b$.$ What portion of the total master $($static$)$ budget variance is attributable to actual sales volume being different from planned sales volume?

c$.$ What portion of the total variance is due to a combination of selling price and costs $($variable cost per unit and total fixed costs$)$ being different from budgeted amounts?