How do you write a number in exponents

You write a number in exponents like this 1 [(9+8)-5]

Exponential Notation is an easier way to write a number as a product of many factors. The exponent tells us how many times the base is used as a factor. 

Now onto the actual problem.

First, you can factor out 625 using the "tree" method or the "ladder" method.

625
/    \
5   125
     /    \
    5    25
          /  \
         5  5

This means you can say that 625=5 to the power of 4.
If your problem requires you only use whole intergers with exponents, then that would be the only way.
If not you can do, 625 = 25*5²

Hope this helps you =)