16 (xx²): (xx³);

16. $$(x^4 \cdot x^2) : (x^5 \cdot x^3) = x^{4+2} : x^{5+3} = x^6 : x^8 = x^{6-8} = x^{-2} = \frac{1}{x^2}$$

Ответ: $$\frac{1}{x^2}$$