Given the following half-reactions and their respective standardreduction potentials 

1.) Cu3+ + 2e- ---> Cu+....E1= 1.128V 

2.)Cu2+ + e- ---> Cu+....E2=0.15V 

3.) Cu2+ + 2e- --->Cu(s)....E3=0.34V 

4.) Cu3+ + 2e- ---> Cu+....E4=0.52V 

calculate the standard reduction potential for the reduction half-reaction of Cu(III) to Cu(II). Cu3+ + e- ---> Cu2+ E= ? V