For parameter kkk, the expression kx−k\frac{k}{x - k}x−kk has a vertical asymptote at x=4x = 4x=4. Find kkk.
k=4k = 4k=4
k=−4k = -4k=−4
k=0k = 0k=0
k=14k = \frac{1}{4}k=41