[latex] frac{sqrt{z}-sqrt{b}}{sqrt{z}-frac{11}{4}}= frac{sqrt{frac{1}{4}}-sqrt{frac{81}{16}}}{sqrt{frac{1}{4}}-frac{11}{4}} = frac{frac{1}{2}-frac{9}{4}}{frac{1}{2}-frac{11}{4}} = frac{(2-9)cdot 4}{4cdot (2-11)} = frac{-7}{-9}=frac{7}{9} [/latex]