Consider a discrete-time LTI system defined by the following difference equation?

3 = X(z) + 7X(z)/z
X(z) (1 + 7/z) = 3
X(z) = 3z / (z+7)
x(n) = 3*(-7)^n * u(n)

Thus y(n) = 3*(-7)^n * u(n) - 3*(-7)^(n) * u(n-1) = 3 delta(n)