Physics Energy in EM waves?

[Bla]

The magnetic field in a traveling EM wave has an rms strength of 40.3 nT. How long does it take to deliver 220 J of energy to 1.40 cm2 of a wall that it hits perpendicularly? (in days )
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here is how I would do it:
B= 40.3nT
A=1.40cm2=1.96e-4 m2
U=220J

S=cB2/mo

(3e8)(40.3e-9)2/ 4pi x10-7
=0.3877 W/m2
t= U/AS
t=220J/(1.96e-4)(0.3877)
t=2895148.258s=33.5days

I've try 33 and 34 and 33.5
But, the system still tells me that it's the wrong answer. Help?