\[\boxed{\mathbf{2}\mathbf{.}\mathbf{93}}\]
\[\textbf{а)}\ 40 + 20 = 60\ :20 = 3 \cdot 9 =\]
\[= 27 + 13 = 40\]
\[\textbf{б)}\ 50 + 40 = 90\ :3 = 30 + 24 =\]
\[= 54\ :9 = 6\]
\[\textbf{в)}\ 100 - 70 = 30 \cdot 8 =\]
\[= 240\ :20 = 12 + 28 = 40\]
\[\textbf{г)}\ 90 - 60 = 30\ :15 =\]
\[= 2 + 14 = 16 \cdot 5 = 80\]