Let the points be A(2, 3), B(4, a) and C(6, – 3).Since the given points are collinear.Area of a triangle = 0 (0.5 mark)Area of ΔABC = 12[(x1y2 +x2y3 + x3y1) − (x2y1 + x3y2 + x1y3)] (0.5 mark)12[(2a − 12 + 18) − (12 + 6a − 6)] = 02a + 6 – (6 + 6a) = 02a + 6 – 6 – 6a = 0– 4a = 0⇒ a = 0∴The value of a = 0 (1 mark)