Separate the right side

\(3+\sin \theta= 3-\frac{\sqrt{2}}{2}\)

Substruct 3 from both sides

\(\sin \theta= -\frac{\sqrt{2}}{2}\)

The reference angle is \(\theta'=45°\) since \(45°=\frac{\sqrt{2}}{2}\). Recall that sine is negative on QIII and QIV.

The QIII solution is

\(\theta=180°+\theta'=180°+45°\)

\(\theta=225°\)

The QIV solution is

\(\theta=360°-\theta'=360°-45°\)

\(\theta=315\)°