How to compute the normals at vertices of a mesh face in C#

Hello everyone,
I have a simple quad mesh face and I want to retrieve the for normals of the vertices (shown in the Image) using c#. I used mesh.NormalAt(x,x,x,x), but this command as output gives me only one normal which seems to be the average of other for normals. Any idea?

use -> m.Normals[meshvertexIndex]
instead of m.NormalAt() which is is a normal of the face at specific parameters

Thank you very much Petras. Problem solved. Just one more question. as return it gives me a vector3f which does not make me able to multiply it by a doube. is there any way to scale the returned vectors?

either cast to to vector3d by (Vector3d)yourvector or multiiply by float