Set rotation.y to be opposite of another objects rotation.y?

I have two objects, ObjectA has a rotation.y of 30 degrees,
I want objectB to at all times have the opposite rotation.y of ObjectA (so in this case -30 or 330 degrees)

I tried this but it didn’t work:

Tail1.transform.localRotation = new Quaternion(Tail1.transform.localRotation.x, Tail1.transform.localRotation.y * -1, Tail1.transform.localRotation.z, Tail1.transform.localRotation.w)

I tried the same above with eulerAngles but that didn’t work either.

Any ideas?

Multiply the Y rotation of object A by Vector3.down (the opposite direction)

transform.rotation = Quaternion.Euler(Vector3.down * objA.eulerAngles.y);