Alright, from what you are given you can write an equation:
"x" can represent the largest of the number
"x-1" can represent the second largest of the number, only one less than the largest
"x-2" can represent the smallest of the number
So we have the equation:
(x-2) + (x-1) + x = 72
Combine like terms:
3x - 3 = 72
3x = 75
x = 25
Remember that x is the largest number, which is 25
to find the smallest, we can plug 25 back into the "x-2" equation, which represent the smallest number
25 - 2 = 23
So the smallest number is 23