Find $\mathbf a \cdot \mathbf b$ if $\mathbf a = \langle -3, 1, -3 \rangle$ and $\mathbf b = \langle 3, 5, 0 \rangle$

$\mathbf a \cdot \mathbf b =$
Is the angle between the vectors "acute", "obtuse" or "right"?