THE BEST ANSWER IS B. FIRST DIGIT IS 1, THE SECOND IS 2, THE THIRD...

28. The best answer is B. First digit is 1, the second is 2, the third can be (7,8,9), the forth can be (0,3,6,9), the fifth and the sixth are dependent with one another. The fifth one is 3 times bigger than the sixth one, therefore there are only 3 options there: (1,3), (2,6), (3,9). All together there are: 1 x 1 x 3 x 4 x 3 = 36 options.