a) $\frac{9}{11}$ +($\frac{-2}{5}$ + $\frac{1}{6}$): $\frac{11}{30}$
= $\frac{9}{11}$ + $\frac{-7}{30}$ . $\frac{30}{11}$
= $\frac{9}{11}$ + $\frac{-7}{11}$
= $\frac{9-7}{11}$
= $\frac{2}{11}$
b) ($\frac{1}{3}$ - $\frac{5}{4}$)^2 : $\frac{77}{144}$
= $\frac{-11}{12}$ ^2 . $\frac{144}{77}$
= $\frac{121}{144}$ . $\frac{144}{77}$
= $\frac{11}{7}$