Fabio Corporation is considering eliminating a department that has a contribution margin of $30,000 and $60,000 in fixed costs. Of the fixed costs, $15,000 cannot be avoided. The effect of eliminating this department on Fabio's overall net operating income would be:

A. a decrease of $30,000.

B. an increase of $30,000.

C. a decrease of $15,000.

D. an increase of $15,000.