$$\begin{gathered} \mathrm{Let} \stackrel{\rightharpoonup }{\mathrm{a}}=\hat{\mathrm{i}}-\hat{\mathrm{j}}, \stackrel{\rightharpoonup }{\mathrm{b}}=\hat{\mathrm{i}}+\hat{\mathrm{j}}+\hat{\mathrm{k}} \mathrm{and} \stackrel{\rightharpoonup }{\mathrm{c}} \\ \mathrm{be} \mathrm{a} \mathrm{vector} \mathrm{such} \mathrm{that} \stackrel{\rightharpoonup }{\mathrm{a}}\times \stackrel{\rightharpoonup }{\mathrm{c}}+\stackrel{\rightharpoonup }{\mathrm{b}}=\stackrel{\rightharpoonup }{0} \\ \mathrm{and} \stackrel{\rightharpoonup }{\mathrm{a}}.\stackrel{\rightharpoonup }{\mathrm{c}}=4, \mathrm{then} {\left|\stackrel{\rightharpoonup }{\mathrm{c}}\right|}^2 \\ \mathrm{is} \mathrm{equal} \mathrm{to} : \end{gathered}$$

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