If n stands for the smallest number, then the second and third number would be (n + 1) and (n + 2)
Write the equation based on what are given
the sum of three numbers = 72
n + (n + 1) + (n + 2) = 72
Then, solve the equation
n + (n + 1) + (n + 2) = 72
3n + 3 = 72
3n = 72 - 3
3n = 69
n = 69/3
n = 23
The smallest number is 23