The incentre of the triangle formed by (0, 0), (5,12), (16, 12) is
(7,9)
(9,7)
(-9, 7)
(-7,9)
Obviously a = 11, b = 20, c = 13.
Hence incentre is
(11×0+20×5+13×1611+20+13,11×0+20×12+13×1211+20+13)
i.e. (7, 9).