$$\frac{n^5}{n^{12} \cdot n^4} = \frac{n^5}{n^{16}} = n^{5-16} = n^{-11}$$
Если $$n = 64$$, то:
$$64^{-11} = (2^6)^{-11} = 2^{-66} = \frac{1}{2^{66}}$$
Ответ: 1/2^66