Answer:
The answer is "-72 k".
Explanation:
Please find the complete question in the attached file.
Given point:
[tex]A=(0,0,0)\\B=(0,8,0)\\C=(9,8,0)\\D=(9,0,0)[/tex]
[tex]\bar{AB} = (0i+8j+0k)-(0i+0j+0k)= 8j\\\\\bar{AC} = (9i+8j+0k)-(0i+0j+0k)= 9i+8j\\\\[/tex]
Calculating the area:
[tex]Area=\left|\begin{array}{ccc}i&j&k\\0&8&0\\9&8&0\end{array}\right|[/tex]
[tex]=i[8(0)-8(0)]-j[(0-0)]+k[(0-9(8))]\\\\=i[0-0]-j[(0)]+k[(0-72)]\\\\=i[0]-j[(0)]+k[(-72)]\\\\=-72 \ k[/tex]