The modulus of $ z $ is:
$$ |z| = 10 \sqrt{ 2 }$$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 = 10 $ and $ b = 10 $ so:
$$ \begin{aligned}|z| &= \sqrt{ 10^2 + 10^2 } \\[1 em]|z| &= \sqrt{ 100 + 100 } \\[1 em]|z| &= \sqrt{ 200 } \\[1 em]|z| &= 10 \sqrt{ 2 } \\[1 em] \end{aligned} $$