Final answer:
To solve the equation X - 21 = 12, we add 21 to both sides and find that X equals 33.
Step-by-step explanation:
The equation given is X - 21 = 12. To find the value of X, we need to isolate X on one side of the equation. This can be done by adding 21 to both sides of the equation, which gives us:
X - 21 + 21 = 12 + 21
So, X = 33.
Therefore, the value of X that satisfies the equation is 33, which corresponds to option (c).