\[\boxed{\mathbf{3.}\mathbf{50}}\]
\[\textbf{а)}\ 119 + z = 246 - 78\]
\[119 + z = 188\]
\[z = 188 - 119\]
\[z = 69.\]
\[\textbf{б)}\ 135 + z - 75 = 85\]
\[z = 85 + 75 - 135\]
\[z = 25.\]
\[\textbf{в)}\ 123 - z - 33 = 44\]
\[123 - z = 44 + 33\]
\[z = 123 - 77\]
\[z = 46.\]
\[\textbf{г)}\ 58 + z + 79 = 167\]
\[z = 167 - 137\]
\[z = 30.\]