Let \( \vec{a}=\hat{i}-\hat{j}+2\hat{k} \) and let \( \vec{b} \) be a vector such that \( \vec{a}\times\vec{b}=2\hat{i}-\hat{k} \) and \( \vec{a}\cdot\vec{b}=3 \). Then the projection of \( \vec{b} \) on the vector \( \vec{a}-\vec{b} \) is:
\( \dfrac{2}{\sqrt{21}} \)
\( 2\sqrt{\dfrac{3}{7}} \)
\( \dfrac{2}{2}{\sqrt{\dfrac{7}{3}}} \)
\( \dfrac{2}{3} \)
