\[\boxed{\mathbf{6.63}}\]
\[\textbf{а)}\ 34 - 90 = - 56\ :( - 14) =\]
\[= 4 \cdot ( - 15) = - 60 + 39 = - 21\]
\[\textbf{б)} - 23 - 29 = - 52\ :( - 13) =\]
\[= 4 \cdot ( - 17) = - 68 - 32 = - 100\]
\[\textbf{в)} - 14 \cdot ( - 7) = 98\ :( - 2) =\]
\[= - 49 - 2 = - 51\ :17 = - 3\]
\[\textbf{г)}\ 45 - 90 = - 45\ :( - 15) =\]
\[= 3 \cdot ( - 17) = - 51 - 49 = - 100\]