1st number : x
2nd number : x + 1
3rd number : x + 2
x + x + 1 + x + 2 = 12
3x + 3 = 12
3x = 9
x = 3
1st number : x = 3
2nd number : x + 1 = 3 + 1 = 4
3rd number : x + 2 = 3 + 2 = 5
The number is 345.
Check :
x + x + 1 + x + 2 = 12
3 + 3 + 1 + 3 + 2 = 12
12 = 12
3 + 4 + 5 = 12
