how to solve this differential equation ?

can anyone please tell me how can i solve this differential equation
i tried laplace appraoch but got stuck in finding laplace of y(t) whole cube term in equation

differential equation

double derivative of y(t) + (4/3)y(t) whole cube= -(1/3)u(t)
where u(t)=sin(3t)
and initial conditions y(0)=0,
first derivative of y(0)=1

i am new to these forums if anyone can telll me how can i write down equations here in their orginal form
as i used it here wording form then it will be great enough .................

Thankx.........