\[\boxed{\mathbf{3.}\mathbf{117}}\]
\[\textbf{а)}\ (x - 87) - 27 = 36\]
\[x - 87 = 36 + 27\]
\[x = 63 + 87\]
\[x = 150.\]
\[\textbf{б)}\ 87 - (41 + y) = 22\]
\[41 + y = 87 - 22\]
\[y = 65 - 41\]
\[y = 24.\]
\[\textbf{в)}\ (764 + y) - 64 = 800\]
\[764 + y - 64 = 800\]
\[700 + y = 800\]
\[y = 800 - 700\]
\[y = 100.\]
\[\textbf{г)}\ (s + 391) - 391 = 834\ \]
\[s + 391 - 391 = 834\]
\[s + 0 = 834\]
\[s = 834.\]