CONCEPT: The question uses the concepts of Probability .
The probability of the faces are proportional to the numbers on them,
=>Let the probabilities of faces bearing 1,2,6 be x,2x,......,6x respectively.
Since one of the faces must occur, we have
Thus, the probability of an even number =2x+4x+6x= 12x=12* (1/21) =4/7 (OPTION D)