Problem Solving

Hi guys,

Can anyone tell me what I am doing wrong here?

I solve a problem and I get the following equation.

-a^2 + ca
------------
1+3c

in the answer choices, this is not an answer and the correct answer is this

a^2 - ac
- ----------------
3c + 1


please note that there is a negative sign at the beginning of the equation.

my understanding is that we should multiply both the top and bottom by

-1
-----
-1

but in that case the bottom should also change the sign.

Any help is greatly appreciated.

Thanks