In this question they are generous enough to give you a set in which your 3-digit number can be, anywhere between 200 and 225. Now, we know the next number is a 1-digit number. Since the product of these numbers is positive, that eliminates the possibility of the 1-digit number being negative. This means your 1-digit number is any number between 0 and 9.
By process of elimination, you can so some simple math to find your answer.
If the 1-digit number is 1: 216+1=217 but 216×1=216, not 624.
If the 1-digit number is 2: 215+2=217 but 215×2=430
Now, if the 1-digit number is 3: 214+3=217 and 214×3=624.
So your numbers are 214 and 3!
