\[\boxed{\mathbf{368}\mathbf{.}}\]
\[1)\log_{15}225 = \log_{15}15^{2} = 2\]
\[2)\log_{4}256 = \log_{4}4^{4} = 4\]
\[3)\log_{3}\frac{1}{243} = \log_{3}\frac{1}{3^{5}} =\]
\[= \log_{3}3^{- 5} = - 5\]
\[4)\log_{7}\frac{1}{343} = \log_{7}\frac{1}{7^{3}} =\]
\[= \log_{7}7^{- 3} = - 3\]