A responsibility center's contribution margin ratio is 40%, and its common fixed costs are currently $100,000. If the center's sales increase by $300,000 and its common fixed costs increase by...

A responsibility center's contribution margin ratio is 40%, and its common fixed costs are currently $100,000. If the center's sales increase by $300,000 and its common fixed costs increase by $20,000, its responsibility margin will increase by $_?

-Why is the answer $100,000?