A 150kVA, 2080/208V, 60Hz, Y/Y connected, three-phase, step-down transformer consists of three identical single-phase transformers. Each transformer has the following parameter values: Rl = 0.45-ohm, Xl = 2.2-ohm , R2 = 4.5m-ohm , X2 = 22m-ohm, RCl = 10k-ohm, and Xml = 8k-ohm. The load on the transformer is 120kVA, 90kW (lagging) at the rated terminal voltage. Determine: a) the primary voltage, and b) the efficiency of the three-phase transformer.