A 25-kVA, 2400/240-V, 60-Hz, single-phase transformer has an equivalent series impedance of 3.45 + j5.75 Ω referred to the primary high voltage side. The core loss is 120 W. When the transformer is delivering rated kVA to a load at rated secondary voltage and a 0.85 lagging power factor, find the percent voltage regulation and the efficiency of the transformer.