Mathematics

The key is to rewrite everything as powers of $3$ so the exponent rules do the work for you. Since $81 = 3^4$ and $9 = 3^2$, you can convert each term, then use the rules that $a^m \times a^n = a^{m+n}$ and $a^m \div a^n = a^{m-n}$ to combine the exponents. This turns a messy expression into simple arithmetic on the exponents.

The key is to rewrite everything as powers of $3$ so the exponent rules do the work for you. Since $81 = 3^4$ and $9 = 3^2$, you can convert each term, then use the rules that $a^m \times a^n = a^{m+n}$ and $a^m \div a^n = a^{m-n}$ to combine the exponents. This turns a messy expression into simple arithmetic on the exponents.