Which of the given number triads has same relationship between them as does 6, 42, 336?

​6, 42, 336

Logic: 1st × 6 + 1st = 2nd and 2nd × 8  = 3rd Number 

​6, 42, 336 → 6 × 6 + 6 = 36 + 6 = 42 and 42 × 8 = 336

From the given options- 

(a) 4, 28, 224 → 4 × 6 + 4 = 24 + 4 = 28 and 28 × 8 = 224 = 224

(b) 2, 4, 642 → 2 × 6 + 2 = 12 + 2 = 14 ≠ 4 and 4 × 8 = 32 ≠ 642

(c) 7, 21, 106 → 7 × 6 + 7 = 42 + 7 = 49 ≠ 21 and 21 × 8 = 168 ≠ 106

(d) 9, 6, 224 → 9 × 6 + 9 = 54 + 9 = 63 ≠ 6 and 6 × 8 = 48 ≠ 224

Correct answer is (a).