Two different positions of the same dice are given below. Which is the number on the face opposite to the face containing 6?

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Logic: In these types of dice problems, we should write all three numbers/letters in clockwise or anticlockwise from a fix common number / letter.

3 is the common digit in both dices.

So, the opposite of the 6 will be 3.

Thus, the correct option is (a) 3.