Hello,

Since vectors a and b are not colinear, they define a plane.

If you make the cross product between them two, you will get a vectordperpendicular to them two, that is, by extension, a vector orthogonal to the plane they form.

Thus, once you have the coordinates ofd, find vector c such that its scalar product withdis 0, because any vector in this plane will be orthogonal tod.

Since you already have 2 coordinates of c, it will be easy