Find the equation of the line passing through the point P (2,5) and:
a. parallel to the line passing through the points A (3, 1) and B(-1,3).
b. parallel to the line l: x + y = 2.
c. perpendicular to the line joining the points A (-1,2) and B (4,-2).
c. perpendicular to the line l: y = x + 1.