\[\boxed{\mathbf{89}\mathbf{.}}\]
\[= \frac{2a^{2} - 2b^{\frac{3}{2}}a^{\frac{1}{2}} - 2a^{\frac{3}{2}}b^{\frac{1}{2}} + 2b^{2}}{a^{\frac{3}{2}} - b^{\frac{3}{2}}} =\]
\[= \frac{2a^{\frac{1}{2}}\left( a^{\frac{3}{2}} - b^{\frac{3}{2}} \right) - 2b^{\frac{1}{2}}\left( a^{\frac{3}{2}} - b^{\frac{3}{2}} \right)}{a^{\frac{3}{2}} - b^{\frac{3}{2}}} =\]
\[= 2a^{\frac{1}{2}} - 2b^{\frac{1}{2}} = 2\left( a^{\frac{1}{2}} - b^{\frac{1}{2}} \right) =\]
\[= 2\left( \sqrt{a} - \sqrt{b} \right)\]