Answer: The correct option is
(C) If a number is not divisible by 3, then it is not divisible by 6.
Step-by-step explanation: We are given to determine the contrapositive of the following statement :
"If a number is divisible by 6, then it is divisible by 3".
We know that
the contrapositive of a conditional statement "if p, then q" is given by
"if not q, then not p".
Therefore, the contrapositive of the given conditional statement is given by
"If a number is not divisible by 3, then it is not divisible by 6".
Thus, (C) is the correct option.