phy--resistance

It is a tricky question as you realise that resistance of ammeter is assumed to be zero. In the diagram, the ammeter is connected in parallel with the two resistor, so all current passes through the ammeter and none passes through the two resistor, so we can treat the diagram having only one resistor.

Since the total voltage of resistors equals to supply voltage(as they are in series), the voltmeter reading should be 3V.

By V = I R, where V is the potential difference, I is the current, and R is the resistance.
3 = I (1)
I = 3A

The reading of ammeter should be 3A.

Feel free to ask questions~!