ABCD is a quadrilateral with angle ABC a right angle. D lies on the perpendicular bisector of AB. The coordinates of A and B are (7, 2) and (2, 5) respectively. The equation of line AD is y=4x-26.

I've already found the equation of the perpendicular bisector of line segment AB, which is y=5/3x-4

a) Find the coordinates of point D.

b) Find the gradient of line BC.

c) Find the value of the second coordinate c of the point C(8, c).

d) Find the area of quadrilateral ABCD.

Thanks in advance.