Given,
The quadrilateral ABCD with vertices A(2,1,1),B(1,2,5),C(−2,−3,5) and D(1,−6,−7)
Now finding, AB=−i^+j^+4k^ and AD=−i^−7j^−8k^
And plotting the diagram we get,

Now we know that,
Area of ΔABD is given by,
=21∣i^−1−1j^1−7k^48∣
=∣10i^−6j^+4k^∣=238
Now finding, CB=3i^+5j^ and CD=3i^−3j^−12k^
So, Area of ΔCBD=21∣i^33j^−35k^−120∣
=∣6(5i^−3j^−2k^)∣
=638
∴ Area of quadrilateral ABCD=838 square units