Course 4 Week 3 Wrong Answer in Quiz

The answer to the question
“If you build a neural network that inputs a picture of a person’s face and outputs N landmarks on the face (assume the input image always contains exactly one face), how many output units will the network have?”
should be 3N according to me: For each landmark, there will be one probability, one x-coordinate & a y-coordinate. So, 3N in total.
But it’s showing that as wrong & it seems that 2N is given as the right answer. Is that right? Can anyone please explain?

if you refer to the lessons, it doesn’t include the probability, or rather they are supposed to be certain. Only x,y coordinates are needed

It is just a landmark, landmark~point; how can we say the probability of being point? So the correct answer is 2N

Same doubt here. Have you find a convincing answer in the meanwhile?