use superposition:

for v1: -3x amp in series with voltage divider in series with 4x amp

for v2: voltage divider (reversed ratio) in series with 4x amp

Edit:

It will be clearer if you forget about the last opamp. this is just a x4 amplifier.

You already figured out vo1, and v2 is a given. Therefore what will be the voltage at the positive input?