Modulus of a Complex Number

Consider the complex number $z$ defined as follows:

$$ z = 3 - 4i $$

Calculate the modulus (magnitude) of the complex number $z$ and express your answer as a rational number. The modulus of a complex number $a + bi$ is computed using the formula:

$$ |z| = ext{sqrt}(a^2 + b^2) $$

Substitute the appropriate values for $a$ and $b$ based on the definition of $z$. Then, provide your answer in both decimal and fractional form (if applicable) as a grid-in response.