#### Answer

$-2$

#### Work Step by Step

$\left( \dfrac {2}{3}\right) ^{x}=\dfrac {9}{4}\Rightarrow \left( \dfrac {2}{3}\right) ^{x}=\left( \dfrac {3}{2}\right) ^{2}\Rightarrow \left( \dfrac {2}{3}\right) ^{x}=\left( \dfrac {2}{3}\right) ^{-2}\Rightarrow x=-2$