Ответ:

а) \(1\frac{5}{19}=\frac{24}{19}\), а \(3\frac{5}{8}=\frac{29}{8}\).

\[\frac{24}{19}\cdot\left(6-\frac{29}{8}\right)=\frac{24}{19}\cdot\frac{19}{8}=3.\]

б) \[\left(6.3:1.4-2.05\right)\cdot1.8=\left(4.5-2.05\right)\cdot1.8=2.45\cdot1.8=4.41.\]

Ответ: а) 3; б) 4,41.