If the area of square ABCD is 36, what is the area of

∆ABC which lies inside square ABCD?

NOTE:

Point Q(2,5) lies on CD of square ABCD.

Point P(6,9) lies on BC on square ABCD.

Point A of ∆ABC coincides with point A of square ABCD.

I determined the area to be 21 but the text book tells me that the answer is 16.

What did I do wrong?

I hope this information is clearly stated here.

Thanks