The total cost of operating the Milling Department for the current period is:

A) $14,280.
B) $15,912.
C) $76,500.
D) $90,780.
E) $92,412.

First, we need to allocate the costs of the Payroll Department and the Maintenance Department to the operating departments.

Payroll Department:
- The total number of employees in the company is 350 (150 in Department A, 100 in Department B, and 100 in Department C).
- Department A receives 40% of the Payroll Department cost = $28,000 x 0.40 = $11,200
- Department B receives 30% of the Payroll Department cost = $28,000 x 0.30 = $8,400
- Department C receives 30% of the Payroll Department cost = $28,000 x 0.30 = $8,400

Maintenance Department:
- The total floor space in the company is 10,000 square feet (6,000 for Department A and 4,000 for Department B).
- Department A receives 60% of the Maintenance Department cost = $24,000 x 0.60 = $14,400
- Department B receives 40% of the Maintenance Department cost = $24,000 x 0.40 = $9,600

Now, we can calculate the total cost of each operating department:
- Department A:
- Direct costs = $42,000 + $28,000 + $14,400 = $84,400
- Indirect costs = $11,200 (Payroll) + $14,400 (Maintenance) = $25,600
- Total cost = $110,000
- Department B:
- Direct costs = $30,000 + $18,000 + $9,600 = $57,600
- Indirect costs = $8,400 (Payroll) + $9,600 (Maintenance) = $18,000
- Total cost = $75,600

Finally, we can calculate the total cost of the Milling Department:
- Direct costs = $45,000
- Indirect costs = $25,600 (Payroll) + $0 (Maintenance) = $25,600
- Total cost = $70,600

Therefore, the answer is E) $92,412. None of the given choices are correct.