Help me with these 3 questions, thank you

1. Records for XYZ, Inc. show the following results for the most recent year:

Sales (16,000 units) $256,000

Variable costs $160,000

Net operating income $32,000

The marginal contribution per unit presented by XYZ is:

a. $4

b. $16

c. $6

d. $2

2. One of the disadvantages of using return on investment (ROI) for a manager's performance evaluation is:

a. All the alternatives are disadvantages of using ROI

b. Postpone the cost of maintenance of the machinery

c. Postponement of the acquisition of necessary assets

d. Replacing obsolete assets too late

3. ABC has the following information available for one of its divisions for the current year:

Sales $15,OOO

Operating expenses 6,500

Average balance of operating assets 5,000

XYZ requires its divisions to make a minimum return of 30%. What is the residual income from that division?

a. $ 7,000.

b. $ 5,000.

c. $ 3,500.

d. $ 2,550.