$a)3,375+4\frac{1}{6}-2\frac{2}{3}=3\frac{3}{8}+3\frac{7}{6}-2\frac{4}{6}=3\frac{3}{8}+1\frac{3}{6}=3\frac{3}{8}+1\frac{1}{2}=$

$=3\frac{3}{8}+1\frac{4}{8}=4\frac{7}{8}$

$b)10\frac{2}{3}-4\frac{7}{8}+\frac{5}{6}=10\frac{16}{24}-4\frac{21}{24}+\frac{20}{24}=10\frac{36}{24}-4\frac{21}{24}=$