A spatial quadrilateral is equivalent to the diagonal of a folded quadrilateral, that is, two planar triangles are not on the same plane.

There may be something you haven't learned. This topic should be done by cosine theorem. Let M N be parallel lines of AD BC.

All three sides of the triangle know that NF=2 MF=3 MN= = root number 19.

Cosine theorem formula c in triangle? =a？ +b？ -2abcosα(α (α is the angle between ab and three sides of abc triangle)

So there is MN? =NF？ +MF？ -2NFMFcos∠NFM

19=4+9-2*2*3cos∠NFM

19 = 13- 12cos∠NFM

12cos∠NFM=-6

cos∠NFM=- 1/2

So ∠ nfm = 120.

His complementary angle is 60 degrees between AD and BC.