the given lines are in the form r = c + k(b) where 'c' is a point on the given line and b is a parallel vector to given line do you find the angle between the parallel vectors of the two given lines which would give you the answer
that is, if i consider 'A' to be the angle between the given lines and 'c' , 'b' to be the parallel vectors to the given line then
cosA = [c.b]/[(c)*(b)] where (c),(b) are the magnitude of the corresponding vectors. = [(1i + 2j + 2k).(3i + 2j + 6k)]/(3*7) = 19/21
that is the angle is cos-1(19/21) which is acute if you wish to have the obtuse angle between the line its cos-1(-19/21)
Note :- this is defined only in case of angle b/w lines in the case of vectors since there is importance in direction we must only consider the angle which is obtained after the direct application of the above formula
hope it helps :)
