High Order Coupled PDE

I have 4th order PDE which is broken into 2 second order PDE and i need to solve them in COMSOL. I tried using general form/coeff form pde of COMSOL but unfortunately i couldnt get results.

Here are the PDE with BCs

PDE 1: d2p/dx2 +dy/dt=0 PDE 2: d2y/dx2=p

At x=0 y=0; dy/dx=sin(100t)

At x=L d2y/dx2=0 d3y/dx3=0

2BC will be entered as dirichlet and 2 as flux/source term.

Any help would be a great favor to me.