Hey guys.

I'm trying to get to the inhomogeneous electromagnetic wave equation for themagnetic field, this is what I've done so far

http://img175.imageshack.us/img175/1797/tmp001.jpg

My problem is that I don't know how to express the expression I marked in red with the magnetic field so I'm pretty much stuck on this one...

can I please have some help?

Thanks a lot.