A local referendum passed by 137 votes. If 993 votes were cast, how many voters voted against the referendum?

I did this:

(x+137)+x=993

2x+137=993

2x=(993-137)

2x=856

2x/2=856/2 = x=428

428 voters voted against the referendum.

Is that correct? Please? I'm hoping it is...*fingers crossed*

Thanks!