23 The diagram shows the three lines x = 8, x + y = 21 and 2y = 12 + x which intersect at the points A, B and C. (a) Find the coordinates of B. (b) The region inside triangle ABC is defined by three inequalities. One of these is x + y <21. Write down the other two inequalities. (c) Find the coordinates of the point, with integer coordinates, that is inside triangle ABC.