\[\boxed{\mathbf{798}\mathbf{.}}\]
\[1)\log_{7}5 =\]
\[= \frac{\ln 5}{\ln 7} \approx \frac{1,60943}{1,94591} \approx 0,83\]
\[2)\log_{8}15 =\]
\[= \frac{\ln 15}{\ln 8} \approx \frac{2,70805}{2,07944} \approx 1,30\]
\[3)\log_{0,7}9 =\]
\[= \frac{\ln 9}{\ln{0,7}} \approx \frac{2,19722}{- 0,35667} \approx - 6,16\]
\[4)\log_{1,1}{0,23} =\]
\[= \frac{\ln{0,23}}{\ln{1,1}} \approx \frac{- 1,46968}{0,09531} \approx - 15,42\]