It's hard to tell from the equation you wrote if the expression is
(-x+4)/13 or -x + (4/13)
Either way though the answer will be the same. If you have some expression such as 2/x then it is a problem if x=0 because anything divided by 0 is an undefined quantity.
Therefore, with rational expressions such as (x+2)/(x-1) we do not want to allow the denominator to be 0. Thus, we say that x cannot be any value that would make the denominator 0.
If the expressions was (x+2)/(x-1) then we would say x cannot be 1 because then (x-1)=(1-1)=0 and (x-1) is the denominator.
In the expression you gave in the question, there is no x in the denominator. Thus, we don't have to restrict the values of x at all!