A $200/400$ V, $50$ Hz, two-winding transformer is rated at $20$ kVA. Its windings are connected as an auto-transformer of rating $200/600$ V. A resistive load of $12 \Omega$ is connected to the high voltage ($600$ V) side of the auto-transformer. The value of equivalent load resistance (in Ohm) as seen from low voltage side is _________.