The first thing to do in ANY word problem is to identify and name the potentially relevant variables, preferably in writing so you don't forget.
In this problem, it is rather obvious that there are two unknowns, the starting number and the ending number. That wasn't hard, now was it? So name them AND WRITE THEM DOWN.
s = starting number
e = ending number.
The second step in ANY word problem is to translate the information given in English into mathematical form.
What do YOU get when you do that?