I believe I've figured out a and b, but I don't understand c

Consider the points A(1,2,0), B(1,0,1), C(0,1,-1) and D(1,0,-1)

a) Find the equation of the plane passing through the points A, B, C. Is the point D on this plane?

b)Find a parametric equation for the line passing through D which is perpendicular (the line) to the plane of the triangle ABC.

c) Find the equation of the plane passing through A and D, which is perpendicular to the plane of the triangle ABC. Note: Two planes are perpendicular if their normal vectors are perpendicular.

a)equation of the plane ABC is -3x+y+2z=-1 and D is not on the plane

b)equation of line perpendicular to plane:

x=1-t

y=t

z=-1-2t

and like I said, I have no idea what to do for c