$a)3,75=3\frac{3}{4}=3\frac{6}{8}=\frac{30}{8}$

$b)1\frac{1}{5}=1,2=\frac{12}{10}=\frac{120}{100}$

$c)\frac{12}{15}=\frac{4}{5}=\frac{8}{10}=\frac{80}{100}$

$d)\frac{104}{100}=1,04=1\frac{1}{25}=\frac{26}{25}$

$e)\frac{39}{12}=\frac{13}{4}=3\frac{1}{4}=3,25$

$f)\frac{2125}{1000}=2,125=2\frac{1}{8}=\frac{17}{8}$