$a)\frac{4}{5}-\frac{3}{25}=\frac{20}{25}-\frac{3}{25}=\frac{17}{25}$

$b)\frac{6}{7}-\frac{2}{3}=\frac{18}{21}-\frac{14}{21}=\frac{4}{21}$

$c)1\frac{3}{10}-\frac{1}{6}=1\frac{9}{30}-\frac{5}{30}=1\frac{4}{30}=1\frac{2}{15}$

$d)3\frac{11}{12}-1\frac{3}{8}=3\frac{22}{24}-1\frac{9}{24}=2\frac{13}{24}$