Determine whether f(x)=2x^2 -6x +k has a maximum or minimum value, and determine the maximum or minimum value.
Amaximum value: k
Bminimum value: k
Cmaximum value: k-9/2
Dminimum value: k-9/2
Eminimum value: k+9/2
Amaximum value: k
Bminimum value: k
Cmaximum value: k-9/2
Dminimum value: k-9/2
Eminimum value: k+9/2