Equate the equation to zero.
hence,
k2x3-kx2+3kx-k=0
(x-3) is factor. That means, (x-3) = 0. Hence , x=3 must satisfy the equation. Substituting 3 instead of x in equation,
k^2 * 27 - k*9 + 3k*3 -k =0
27k^2 - 9k + 9k -k =0
27k^2 - k =0
27k^2 = k
27k = 1 ( cancel k on both sides)
k = 1/27.