Inhomogeneous electromagnetic wave equation

[asi123]

1. The problem statement, all variables and given/known data

Hey guys.

I'm trying to get to the inhomogeneous electromagnetic wave equation for the magnetic 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.

2. Relevant equations



3. The attempt at a solution