a) \(3m\; 4dm = 3 \dfrac {4}{10}m = 3,4m \);
\(2m\; 5cm = 2 \dfrac {5}{100}m =2,05m \);
\(21m\; 36cm = 21 \dfrac {36}{100}m =21,36m \);
b) \(8dm\; 7cm = 8 \dfrac {7}{10}dm =8,7dm \);
\(4dm\; 32mm = 4 \dfrac {32}{100}dm =4,32dm \);
\(73mm = \dfrac {73}{100}dm = 0,73 dm \).