Write $\frac{a^{-n}}{b^{-m}}$a−nb−m without negative exponents.
Find the value of $n$n such that $\frac{1}{25}=5^n$125=5n.
Find the value of $n$n such that $\frac{1}{8}=2^n$18=2n.
Evaluate $4\times3^{-2}+8^0$4×3−2+80 without the use of a calculator.