A way to calculate only clockwise angle from a given line

Hi there is there a way to calculate the clockwise angle from a specific line from/towards the line on that point that is parallel to x-axis?a

Answer 1

[Duncan Barclay]

Goggle for the dot product of two vectors.

[Darren Koh]

Hi is there a more straightforward way for this? One of the 'vector' is just the line from the point parallel to x-axis.