Suppose the domain of f is (-1,1). Define the function l by l(x) = f((x - 1)/(x - 3)). What is the domain of l?

So I think that since there is just 2 domains we can substitute it in the function, so I(x)=f(-1-1)/(-1-3))= 1/2, and I(x)=f(1-1)/(1-3))=0, so the 2 possible domains for I is 1/2 and 0. Not sure if this is correct or not.