The modulus of $ z $ is:
$$ |z| = \frac{\sqrt{ 88621 }}{ 410 }$$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 = \frac{ 211 }{ 410 } $ and $ b = \frac{ 21 }{ 41 } $ so:
$$ \begin{aligned}|z| &= \sqrt{ \left(\frac{ 211 }{ 410 }\right)^2 + \left(\frac{ 21 }{ 41 }\right)^2 } \\[1 em]|z| &= \sqrt{ \frac{ 44521 }{ 168100 } + \frac{ 441 }{ 1681 } } \\[1 em]|z| &= \sqrt{ \frac{ 88621 }{ 168100 } } \\[1 em]|z| &= \frac{\sqrt{ 88621 }}{ 410 } \\[1 em] \end{aligned} $$