Input resistance: Check how much current is flowing into input NMOS M1 transistor. Divide input voltage vin by this current to get input resistance.

Voltage gain: Start this questions by first replacing NMOS M1 and input voltage vin by thevenin equivalent circuit. Now draw the small-signal equivalent model of the simplified circuit to obtain voltage gain. DC voltage source VDD needs to be short circuited by calculating the voltage gain.

Output resistance: For the calculation of output resistance, input voltage source and VDD both need to be short circuited. Connect an output voltage vout at output terminal and assume iout current is flowing into the circuit. Dividing vout by iout will give the output resistance.

Another method to calculate output resistance is to divide circuit into up circuit and down circuit at output terminal. Individual resistance at output terminal due to up and down circuit can be calculated. Parallel combination of up and down resistance will be equal to output resistance of the circuit.