Temperature Neutrons: Solve Equations for K

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Homework Statement

see attached

Homework Equations

$$\lambda$$_maxT=2.898*10^-3
$$\lambda$$_medT=4.107*10^-3

The Attempt at a Solution

I have tried both the above equations (12834375K and 9056250K) both are wrong..
not sure where to go?
thanks for any help

 

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Forgot to upload pic!