Find the missing term

Logic:
(Left − Bottom) + constant = Right

Step-by-step:
1st → (18 − 9) + 6 = 15 ✔ → constant = 6
2nd → (12 − 8) + 6 = 10 ✔

Apply:
3rd → (24 − ?) + 6 = 27
24 − ? = 21
? = 3

Short Trick:
(Left − Bottom) + 6 = Right

Final Answer:
3

Final Correct Option:

C