Rule for a factor of a numerator of a denominator with
a negative exponent:

1.  If the factor with the negative exponent is in the NUMERATOR,
    move it to the DENOMINATOR, changing the sign of the exponent 
    to positive.

and vice-verse:

2.  If the factor with the negative exponent is in the DENOMINATOR,
    move it to the NUMERATOR, changing the sign of the exponent 
    to positive.

    


Since there was no other factor in the denominator (other than 1 understood),
we did not need to show a denominator of 1. 

Now we add the exponents and get

       <-- final answer

----------------------------------------------

[However in other problems where the only factor is a negative exponent
(other than 1) we must show the understood 1 factor in the numerator.]

Suppose your problem was:



We would then bring the  to the denominator. But the next step 
would be

 not 

We would have to put the understood 1 factor in the numerator.

And then add the exponents in the denominator:



Edwin