Two AC sources of the same frequency are joined in series…

Step 1. The parts of the second arrow. Along the axis: $45\ \text{V} \times \cos 60^\circ = 22.5$ V. Across the axis: $45\ \text{V} \times \sin 60^\circ = 39.0$ V.

Step 2. The parts of the total. Along the axis: $27\ \text{V} + 22.5\ \text{V} = 49.5$ V. Across the axis: $39.0$ V.

Step 3. The peak value. $V_m = \sqrt{(49.5\ \text{V})^2 + (39.0\ \text{V})^2} = 63.0$ V.

Step 4. The rms value. $V_{rms} = \dfrac{63.0\ \text{V}}{\sqrt{2}} = 44.5$ V.

Step 5. The phase. $\tan \varphi = \dfrac{39.0}{49.5}$, so $\varphi = 38.2^\circ$ ahead of the first source.