Engberg Company installs lawn sod in home yards. The company's most recent monthly contribution format income statement follows:

AmountPercent of Sales

Sales$128,000100%

Variable expenses51,20040%

Contribution margin76,80060%

Fixed expenses18,000

Net operating income$58,800

3. Construct a new contribution format income statement for the company assuming a 10% increase in sales.

Amount Percent of Sales

$140,800 100% (increase of 10% in sales)

Variable expenses 40%

Contribution margin140,800 60%

Fixed expenses18,000

Net operating income

$122,800

I am just stuck at the last part for variable expenses. How do you get the variable expense if sales increase by 10%?