If O is the centre of a circle of radius 5 cm. At a distance of 13 cm from O, a point P is taken. From this point, two tangents PQ and PR are drawn to the circle. Then , the area of quadrilateral PQOR is
P and Q undertook to do a work for Rs 7200. P alone could do it in 20 days and Q alone in 12 days. With the assistance of R they finished the work in 5days. What is the share (in Rs) of R?