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To simplify the expression \( \frac{7^{21}}{7^{18}} \), you can use the properties of exponents. When you divide two exponents with the same base, you subtract the exponents: \[ \frac{a^m}{a^n} = a^{m-n} \] Applying this to your expression: \[ \frac{7^{21}}{7^{18}} = 7^{21-18} = 7^3 \] Now, \( 7^3 \) can be calculated as: \[ 7^3 = 7 \times 7 \times 7 = 343 \] Thus, the simplified expression equates to: \[ \frac{7^{21}}{7^{18}} = 7^3 = 343 \]