What is the value of k?

Step-by-step explanation:

The vertex is (d, e)

for quadratic function: f(x) = ax² + bx + c  we have:

d = -b/a    and    d = (x₁ + x₂)/2  

a = 1,   b = k,   x₁ = -4,    x₂=-2      

so:

d = -b/a = -k/1 = -k   and   d = (x₁ + x₂)/2 = (-4-2)/2 = -3

-k = -3

k = 3