Express the solution of the given initial value problem as a sum of two oscillations. Primes denote derivatives with respect to time t. Graph the solution function x(t) in such a way that you can identify and label its period. x'' + 4x = 9 cos t + 12 sin t; x(0) = 15, x'(0) = 0 Express the solution of the given initial value problem as a sum of two oscillations. x(t) = (Simplify your answer. Type an equation. Type an exact answer, using radicals as needed.) Graph the solution function x(t). Choose the correct graph below.