Simplifying algebraic expression with fraction of polynomials I cannot seem to find a way to simplify the following expression:
$$\frac{9{a}^{4}-{a}^{2}{ b  }^{ 4  }  +16 { b  }^{ 8  }    }{ 3 { a  }^{ 2  }  -5a { b  }^{ 2  }  +4 { b  }^{ 4  }    }$$
I have tried factoring by $a$ and rewriting the division as multiplication with inverse.

The numerator $9a^4 - a^2 b^4 + 16b^8$ factorises as
$(3a^2+4b^4+5ab^2)(3a^2+4b^4−5ab^2)$.
Thus, when the $3a^2+4b^4−5ab^2\not=0$,
$$\frac{9a^4 - a^2 b^4 + 16b^8}{3a^2+4b^4−5ab^2}=   3a^2+4b^4+5ab^2$$
