answer 4.3b
K_c = [CH₃CO₂C₂H₅] [H₂O] / [CH₃CO₂H] [C₂H₅OH]
[C₂H₅OH] = [CH₃CO₂C₂H₅] [H₂O] / [CH₃CO₂H] * K_c  
Let total volume be V so
amount C₂H₅OH/V = amount CH₃CO₂C₂H₅/V amount H₂O/V / amount CH₃CO₂H/V * K_c  
amount C₂H₅OH= amount CH₃CO₂C₂H₅ * amount H₂O / amount CH₃CO₂H * K_c  
amount C₂H₅OH = 0.66 mol * 0.66 mol / 0.33 mol * 4.0  =  0.33 mol