Angle C is 90 degrees. Angle B is such that it allows the side of the box to
stand perpendicular to the table top. Angle A is such that the both sides of
the fingers sit neatly against the slot on both sides of the cut. You'll
have to do the math to come up with the angles that work for your project.
BTW, the saw blade would be left at 90 degrees (or zero) and the blade would
have to be raised high enough above the table to cut the slots.