Unit step response of the system described by y(k) +y(k-1) =3x(k) is where x(k) is input and y(k) is the output:

Select one: a. 3z2/((z+1)(z-1)) b. (3z+3)/(z-1) c. 3z/((z+1)(z-1)) d. (3z(z-1))/(z+1)