\[\boxed{\mathbf{90}.}\]
\[1)\ \frac{x^{2} - 3}{x - \sqrt{3}} =\]
\[= \frac{\left( x - \sqrt{3} \right)\left( x + \sqrt{3} \right)}{x - \sqrt{3}} = x + \sqrt{3}\]
\[2)\ \frac{4b^{2} - 7}{2b + \sqrt{7}} =\]
\[= \frac{\left( 2b - \sqrt{7} \right)\left( 2b + \sqrt{7} \right)}{2b + \sqrt{7}} =\]
\[= 2b - \sqrt{7}\]