\frac{I_2}{I_{2n}} = 0{,}85  \ \Rightarrow\  \frac{I_2}{72} = 0{,}85 \ \Rightarrow\  I_2 = 72 \cdot 0{,}85 = 61{,}2\ \mathrm{A}

 P_2 = \sqrt{3}\, V_2 I_2 \cos\varphi = \sqrt{3}\cdot 400 \cdot 61{,}2 \cdot 0{,}8 = 33{,}92\ \text{kW}

 P_{CU} = \left(\frac{I_2}{I_{2n}}\right)^2 \cdot P_{CC} = 0{,}85^2 \cdot 1100

 \eta = \frac{P_2}{P_2 + P_0 + P_{CU}} = \frac{33920}{33920 + 200 + 0{,}85^2 \cdot 1100} = 0{,}9715