Simplify $\frac{\frac{x^{3}}{y^{3}}-\frac{27}{8}}{\frac{x^{2}}{y^{2}}+\frac{3 x}{2 y}+\frac{18}{8}}$

Simplify: $\frac{\frac{x^{3}}{y^{3}}-\frac{27}{8}}{\frac{x^{2}}{y^{2}}+\frac{3 x}{2 y}+\frac{18}{8}}$