How much is the secondary voltage?
A resistor is connected across the secondary terminals. How much current flows through the resistor?
This current is the secondary current of the transformer. How much is the primary current?
If it is not stated otherwise, you can take the transformer ideal. It means that the power input is equal to the output power.
You know both the voltage and current across the resistor, connected to the output of the transformer. How much is the power on the resistor?
ehild