A Miscalculation #1

This calculator was purchased at Evergreen Office Supplies.  Smudge reprogrammed it so it gives incorrect answers.  Here are some sample answers:

20 ÷ 2 = 18

18 ÷ 2 = 16

18 ÷ 3 = 15

15 ÷ 3 = 12

What will happen when you enter 16 ÷ 4 = ?

a. 14

b. 13

c. 12