\[\boxed{\mathbf{3.}\mathbf{95}}\]
\[\textbf{а)}\ 25z + 71 = 171\]
\[25z = 171 - 71\]
\[z = 100\ :25\]
\[z = 4.\]
\[\textbf{б)}\ 24 + 10t = 134\]
\[10t = 134 - 24\]
\[t = 110\ :10\]
\[t = 11.\]
\[\textbf{в)}\ 8y - 26 = 158\]
\[8y = 158 + 26\]
\[y = 184\ :8\]
\[y = 23.\]
\[\textbf{г)}\ 204 - 9r = 51\]
\[9r = 204 - 51\]
\[r = 153\ :9\]
\[r = 17.\ \]