Answer:

So then the difference of temperature across the material would be 
Explanation:
For this case we can use the Fourier Law of heat conduction given by the following equation:
(1)
Where k = thermal conductivity = 0.2 W/ mK
A= 1m^2 represent the cross sectional area
Q= 3KW represent the rate of heat transfer
is the temperature of difference that we want to find
represent the thickness of the material
If we solve
in absolute value from the equation (1) we got:

First we convert 3KW to W and we got:

And we have everything to replace and we got:

So then the difference of temperature across the material would be 
I would say D. Hope I helped!
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Hope this helps!