In a two-digit number, the digit in the unit's place is three times the digit in tenth's place. The sum of the digits is equal to 8. What is the number?

Let us assume the ten's digit of the number is n. Then the unit's digit will be 3n.
According to question,
The sum of the digits is equal to 8.
sum of the digit = 8
n + 3n = 8
⇒ 4n = 8
⇒ n = 2
So, ten's digit is 2 and unit's digit is 6.
So the number = 10n + 3n = 10 x 2 + 3 x 2 = 20 + 6 = 26.