If I understand this right, is this saying that when 4 is added to the number, the sum of its digits becomesof the sum of the digits of the original number?
If so, then your number is:, since the sum of its digits is 10 (2 + 8), and when 4 is added to the number, the result is 32 (28 + 4), whose digits
sum to 5 (3 + 2), and which is actuallyof 2 + 8, or of 10.