5. (a) An RL circuit is governed by the equation: dI/dt + 20I = 100, t > 0, where I is the current. Solve this equation if I = 4 at t = 0. Find the steady-state current. How long does it take for the current to achieve the value I = 4.5? [5 marks]
(b) Solve the following initial value problem for a function x = x(t): d^2x/dt^2 - 6dx/dt + 10x = 0, t > 0, subject to x(0) = 1, dx/dt(0) = 0. [5 marks]
6. Find the general solution of each of the following nonhomogeneous differential equations: (i) d^2x/dt^2 + 9x = cos t [5 marks] (ii) d^2x/dt^2 + dx/dt - 2x = 3e^t [5 marks]