Write each one on paper and turn the paper upside down.
A)81 becomes 18 when turned upside-down, and decreases by 63, not by 12
B)69 stays 69, and neither decreases nor increases, so it doesn't decrease by 12
C)16 becomes 91 when turned upside-down, and increases by 75, it doesn't decrease by 12
D)98 becomes 86 when turned upside-down, and decreases by 12. So D) is the answer.
Edwin