Vector Calculus

$\nabla \phi = 2x\hat{i} + 2y\hat{j} + 2z\hat{k} = 2\hat{i} + 4\hat{j} + 4\hat{k}$. $|\nabla \phi| = \sqrt{2^2 + 4^2 + 4^2} = \sqrt{4 + 16 + 16} = \sqrt{36} = 6$.