A 50 kVA, 6360V/230V transformer is tested on open and short-circuit to obtain its efficiency. The results of the tests are as follows. Open circuit: primary voltage, 6360V; primary current, 1A; power input, 2 kW. Short circuit: voltage across primary winding, 180V; current in secondary winding, 175A; power input, 2 kW. Find the transformer efficiency when supplying full load at a power factor of 0.8 lagging.