To simplify the expression \( \frac{5^6}{5^3} \) using the quotient rule of exponents, we subtract the exponent in the denominator from the exponent in the numerator:
\[ \frac{5^6}{5^3} = 5^{6-3} = 5^3 \]
So the simplified expression is \( 5^3 \).
The correct response is 5 cubed (or \( 5^3 \)).