  
 Exa-10.4(a)   
The energy of interaction with magnetic field is given by uB and the degeneracy of the states are +-1/2 which are identical.
The ratio is therefore pE2/pE1 which gives e^(-2*u*B/k*T) 
 Ex-10.4(b)   
The value of temperature ar which the given ratio exists is 140.46 K 