Solution:The pattern followed here is :{(1st number - 2nd number) ร 3} = (3rd number - 2nd number)
(12, 8, 20) โ (12 - 8) ร 3 = 12 , (20 - 8) = 12 L.H.S = R.H.S
(7, 3, 15) โ (7 - 3) ร 3 = 12, (15 - 3) = 12 L.H.S = R.H.S
Similarly,
(9, 4, 19) โ (9 - 4) ร 3 = 15, (19 - 4) = 15 L.H.S = R.H.S
Hence, "(9, 4, 19)" is the correct answer.