\[\boxed{\mathbf{19}\mathbf{.}}\]
\[\textbf{а)}\ 6 + 6 - 4 = 12 - 4 = 8\]
\[14 - 5 + 3 = 9 + 3 = 12\]
\[\textbf{б)}\ 5 + 8 + 47 = 13 + 47 = 60\]
\[13 - 9 + 36 = 4 + 36 = 40\]
\[91 + (18 - 9) = 91 + 9 = 100\]
\[50 - (8 + 8) = 50 - 16 = 34\]