$\log_{ 10 }({ 9 })+\log_{ 10 }({ {7}^{-2} })$
Use $\log_{ a }({ x })+\log_{ a }({ y })=\log_{ a }({ x \times y })$ to simplify the expression$\log_{ 10 }({ 9 \times {7}^{-2} })$
Express with a positive exponent using ${a}^{-n}=\frac{ 1 }{ {a}^{n} }$$\log_{ 10 }({ 9 \times \frac{ 1 }{ {7}^{2} } })$
Evaluate the power$\log_{ 10 }({ 9 \times \frac{ 1 }{ 49 } })$
Calculate the product$\log_{ 10 }({ \frac{ 9 }{ 49 } })$
Write the number in exponential form with the base of $\frac{ 3 }{ 7 }$$\log_{ 10 }({ {\left( \frac{ 3 }{ 7 } \right)}^{2} })$
Use $\log_{ a }({ {b}^{c} })=c \times \log_{ a }({ b })$ to transform the expression$\begin{align*}&2\log_{ 10 }({ \frac{ 3 }{ 7 } }) \\&\approx-0.735954\end{align*}$