Differential Equations

Find the value of a for which axcos3x is a particular integral of the differential equation
d^2 / dx^2 + 9 y = -12sin3x

b) Hence find the general solution of this differential equation
The particular solution of the differential equation for which y = 1 and dy/dx = 2 at x = 0 is y = g(x)

c) Find g(x)