Six letters P, Q, R, S, T and U are written on different faces of a dice. Two positions of this dice are shown in the following figure. Find the letter on the face opposite to S.

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Given: ​Six letters P, Q, R, S, T and U are written on different faces of a dice.

Logic:   If two dice have the same face value in the given image then their clockwise or anticlockwise wise number are known as opposite numbers in dice.

R is the opposite to S

Thus, correct option is (a).