3)
[tex]\displaystyle\bf\\1)\\6,15+0,081-3,4=\\=6,231-3,4=\boxed{\bf2,831}\\\\\\2)\\\\\frac{2}{5}\times\frac{1}{2}-\frac{7}{25}:\frac{7}{5}=\\\\\\=\frac{2}{5}\times\frac{1}{2}-\frac{7}{25}\times\frac{5}{7}=\\\\\\=\frac{2\times1}{5\times2}-\frac{7\times5}{25\times7}=\\\\\\=\frac{1}{5}-\frac{5}{25}=\\\\\\=\frac{1}{5}-\frac{1}{5}=\boxed{\bf0}[/tex]
.
[tex]\displaystyle\bf\\3)\\69:3-\{24\times4-5\times[7\times(-6)^2+|5-18|]\}=\\\\=69:3-\{24\times4-5\times[7\times(-6)^2+18-5]\}=\\\\=69:3-\{24\times4-5\times[7\times36+18-5]\}=\\\\=69:3-\{24\times4-5\times[252+18-5]\}=\\\\=69:3-\{24\times4-5\times[270-5]\}=\\\\=69:3-\{24\times4-5\times265\}=\\\\=69:3-\{96-1325\}=\\\\=69:3-\{-1229\}=\\\\=69:3+1229=\\\\=23+1229=\boxed{\bf1252}[/tex]
