The differential equation model for two first-order systems in series is

x(t) + 4x(t) + 3x(t) = u(t), where u(t) is the input of the first system and x(t) is the output of the second system. The response x(t) of the system to a unit impulse u(t) is: 2e-21 a. x(t) e == b. x(t) = - 1 -31 - 3 1 1 c. x(t)= d. x(t) e e-31