Let the smallest number be 'x'
Since, we are considering three consecutive numbers, the other two numbers will be x+1 and x+2.
x+(x+1)+(x+2)=39 ⇒3x+3=39 ⇒3x+3−3=39−3 ⇒3x=36 ⇒3x÷3=36÷3 ⇒x=12
Thus, the three consecutive numbers are 12, 12+1, and 12+2.
So, 12, 13 and 14 are the required numbers.