Angle between two lines with coordinates.

I have two lines AB, BC with known coordinates. they both have a common coordinate at point B.
How to find angle between AB and BC wrt VB6.

any Help for formula for finding angle at B.

this is what i've come up wiht... its not checked>
pi-arctg((xA-xB)/(yA-yB))+arctg((xB-xC)/(yB-yC))

probably doesnt work

Well tan^-1(m_AB) will give the angle (in degrees) of line AB. Do the same for BC, then find the difference.