$ f_n (x) = frac {nx} {1 + n ^ 4x ^ 4} $ , $ x∈ mathbb {R} $

Fix me $ epsilon> 0 $, searching $ delta> 0 $, so for each $ x, and ∈ mho $ with $ | x-y | < delta $ it is valid $ | f (x) -f (y) | < epsilon $.

So: $ | frac {nx} {1 + n ^ 4x ^ 4} – frac {ny} {1 + n ^ 4y ^ 4} | $=$ | frac {n (x-y) + n ^ 5xy (y ^ 3-x ^ 3)} {(1 + n ^ 4x ^ 4) (1 + n ^ 4y ^ 4)} | $

I do not know how I can find a $ delta $Is there something wrong up?