Use the following information to answer the following questions:

Selling price per unit	$100
Variable expense per unit	$40
Fixed expenses per month	$60,000

a. Operating income at a volume of 4,000 units per month is how many dollars?

b. The break-even point in volume of units is how many units?

c: The contribution margin ratio is what percent?

d: If sales volume were to decrease by 10% from the original 4,000 unit volume, operating income would increase/decrease (input the word "increase" or "decrease") by how many dollars?