The modulus of $ z $ is:
$$ |z| = \frac{\sqrt{ 901 }}{ 10 }$$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{ 1 }{ 10 } $ and $ b = 3 $ so:
$$ \begin{aligned}|z| &= \sqrt{ \left(\frac{ 1 }{ 10 }\right)^2 + 3^2 } \\[1 em]|z| &= \sqrt{ \frac{ 1 }{ 100 } + 9 } \\[1 em]|z| &= \sqrt{ \frac{ 901 }{ 100 } } \\[1 em]|z| &= \frac{\sqrt{ 901 }}{ 10 } \\[1 em] \end{aligned} $$