d^2 = (x2 - x1)^2 + (y2 - y1)^2
d^2 = (8 - 4)^2 + (k - 2)^2
d = 5 so
5^2 = 4^2 + k^2 - 4k + 4
25 = 16 + k^2 - 4k + 4
25 = 20 + k^2 - 4k
0 = k^2 - 4k - 5
0 = (k - 5)(k + 1)
k has 2 answers
k - 5 = 0
k = 5
k + 1 = 0
k = - 1
The two answers are
(8, 5) and (8, -1) <<<< answer