Please help with formulas for b and c

Chapter 1: Applying Excel
Data
Sales	$12,000
Variable costs:
Cost of goods sold	$6,000
Variable selling	$900
Variable administrative	$400
Fixed costs:
Fixed selling	$2,500
Fixed administrative	$1,500
Enter a formula into each of the cells marked with a ? below
Exhibit 1-7
Traditional Format Income Statement
Sales		$ 1,200
Cost of goods sold		6,000
Gross margin		6,000
Selling and administrative expenses:
Selling	$ 3,100
Administrative	1,900	5,000
Net operating income		$ 1,000
Contribution Format Income Statement
Sales		$ 12,000
Variable expenses:
Cost of goods sold	$ 6,000
Variable selling	600
Variable administration	400	7,000
Contribution margin		5,000
Fixed expenses:
Fixed selling	2,500
Fixed administrative	1,500	4,000
Net operating income		$ 1,000