Energy in electromagnetic waves

[map7s]

Homework Statement

Find the electric and magnetic field amplitudes in an electromagnetic wave that has an average energy density of 3.0 J/m3.

Homework Equations

u=1/2 eo E^2 + 1/(2uo) B^2
u=eo E^2
u=B^2 /uo

The Attempt at a Solution

I tried using these equations, but I wasn't getting the right answer. Do I have to change the units or am I just using the wrong equations?

 

[map7s]

just kidding...I figured it out :)

 

[Combatchuck]

how do you do it?!