Recreating a curved line

Hi,

I'm just starting out with CAD and DraftSight (trying to teach myself), but I'm under a bit of a time constraint and I need to recreate the attached drawing in DraftSight.

I have no problems with the rectangles but I can't recreate the top curve. I'm not even sure where to start?

Can anybody point me in the right direction.

 

Regards

L.