Give the Formula for Transformers in terms of Power. Why is it like that?

Pd Across the Primary Coil x Current in the Primary Coil = Pd Across the Secondary Coil x Current in the Secondary Coil -This is the Formula because the Power in the Primary Coil = Power in the Secondary Coil [It can be lower in Reality as Energy can be Lost to Surroundings or to Wasted Stores]