Solution:The pattern followed here is :The difference between the 1st term and the 2nd term is the digit sum of the first term and the difference between 2nd term
and 3rd term is the digit sum of the 2nd term.
For (47 : 58 : 71)
⇒ 58 - 47 = 11 = (4 + 7) Digit sum of the first number.
⇒ 71 - 58 = 13 = (5 + 8) Digit sum of the second number.
Similarly, For (72 : 81 : 90)
⇒ 81 - 72 = 9 = (7 + 2) Digit sum of the first number.
⇒ 90 - 81 = 9 = (8 + 1) Digit sum of the second number.