a,$\frac{3}{4}$ -$\frac{5}{6}$ .($\frac{1}{6}$ +$\frac{1}{8}$ ) :($\frac{7}{12}$
= $\frac{3}{4}$ -$\frac{5}{6}$. $\frac{7}{24}$ :$\frac{7}{12}$
= $\frac{3}{4}$- $\frac{5}{6}$ .$\frac{1}{2}$
= $\frac{3}{4}$- $\frac{5}{12}$
= $\frac{1}{3}$
b$\frac{15}{8}$: $\frac{45}{6}$- $\frac{1}{13}$ .($\frac{4}{9}$- $\frac{1}{12}$)
= $\frac{15}{8}$: $\frac{45}{6}$- $\frac{1}{13}$ .$\frac{13}{36}$
= $\frac{1}{4}$ -$\frac{13}{36}$
= $\frac{2}{9}$
