a)
54:(4\frac{1}{2}*1\frac{1}{2})-2\frac{7}{8}=54:(\frac{9*3}{2*2})-2\frac{7}{8}=
=54:\frac{27}{4}-2\frac{7}{8}=54*\frac{4}{27}-2\frac{7}{8}=8-2\frac{7}{8}=5\frac{1}{8}
b)
(2\frac{1}{4}-1\frac{2}{3}):(\frac{1}{6}+\frac{2}{6})=(\frac{9}{4}-\frac{5}{3}):\frac{3}{6}=
=(\frac{27}{12}-\frac{20}{12}):\frac{1}{2}=\frac{7}{12}*\frac{2}{1}=\frac{7}{6}=1\frac{1}{6}