The modulus of $ z $ is:
$$ |z| = \frac{ 1261 \sqrt{ 29}}{ 5000 }$$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{ 1261 }{ 1000 } $ and $ b = -\frac{ 1261 }{ 2500 } $ so:
$$ \begin{aligned}|z| &= \sqrt{ \left(\frac{ 1261 }{ 1000 }\right)^2 + \left(-\frac{ 1261 }{ 2500 }\right)^2 } \\[1 em]|z| &= \sqrt{ \frac{ 1590121 }{ 1000000 } + \frac{ 1590121 }{ 6250000 } } \\[1 em]|z| &= \sqrt{ \frac{ 46113509 }{ 25000000 } } \\[1 em]|z| &= \frac{ 1261 \sqrt{ 29}}{ 5000 } \\[1 em] \end{aligned} $$