The points A, B and $\mathrm{C}$ have position vectors

$\boldsymbol{a}=i-3 j, \quad \boldsymbol{b}=2 i-j+k$ and $\boldsymbol{c}=10 j+10 k$ respectively.

(i) $\quad$ Calculate the product $\boldsymbol{a} .(\boldsymbol{b} \leftarrow \boldsymbol{\varepsilon})$.

(ii) Describe fully the geometrical meaning of this product.