Finding v0 on the right side of an op-amp?
Golden Rules. With negative feedback in place...


No current flows into the input terminals of the opamp
The voltage at the plus terminal equals the voltage at the minus terminal.


Because no current flows into the positive terminal, current must flow from the voltage source, through the series resistors 16 ohm and 24 ohm. So you should be able to figure out that the voltage at the input terminal is 7.5 * 24 / 40 = 4.5V. It follows that the voltage at the negative terminal = 4.5V. Now you've got another voltage divider from the negative terminal through 8 ohms in series with 12 ohms. The voltage across the 12 ohm resistor is therefore 4.5 * 12 / 20 = 2.7V.