Answer:

-19

Step-by-step explanation:

x-3 =0

x=3

then sub x to the given polynomial

6x^3 - kx^2 + 2x + 3 = 0

6(3)^3 + k(3)^2 + 2(3) + 3 = 0

162 + 9k + 6 + 3 = 0

9k = -171

k= -19