The modulus of $ z $ is:
$$ |z| = 2 \sqrt{ 34 }$$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 = -6 $ so:
$$ \begin{aligned}|z| &= \sqrt{ (-10)^2 + (-6)^2 } \\[1 em]|z| &= \sqrt{ 100 + 36 } \\[1 em]|z| &= \sqrt{ 136 } \\[1 em]|z| &= 2 \sqrt{ 34 } \\[1 em] \end{aligned} $$