The modulus of $ z $ is:
$$ |z| = \frac{\sqrt{ 782129 }}{ 20 }$$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 = 40 $ and $ b = \frac{ 377 }{ 20 } $ so:
$$ \begin{aligned}|z| &= \sqrt{ 40^2 + \left(\frac{ 377 }{ 20 }\right)^2 } \\[1 em]|z| &= \sqrt{ 1600 + \frac{ 142129 }{ 400 } } \\[1 em]|z| &= \sqrt{ \frac{ 782129 }{ 400 } } \\[1 em]|z| &= \frac{\sqrt{ 782129 }}{ 20 } \\[1 em] \end{aligned} $$