The modulus of $ z $ is:
$$ |z| = \sqrt{ 6586 }$$To find modulus of a complex number $ z = a + bi $ we use formula:
$$ |z| = \sqrt{a^2 + b^2} $$In this example we have $ a = 31 $ and $ b = 75 $ so:
$$ \begin{aligned}|z| &= \sqrt{ 31^2 + 75^2 } \\[1 em]|z| &= \sqrt{ 961 + 5625 } \\[1 em]|z| &= \sqrt{ 6586 } \\[1 em] \end{aligned} $$