Vector Algebra

If $\bar{a} = \hat{i} - \hat{k}$, $\bar{b} = x\hat{i} + \hat{j} + (1-x)\hat{k}$ and $\bar{c} = y\hat{i} + x\hat{j} + (1+x-y)\hat{k}$ then $[\bar{a}\ \bar{b}\ \bar{c}]$ depends on