Adding two signals and finding the RMS and Peak to peak value of the output signal
For U1 the peak voltage is 4V and so is the RMS as it is DC

For U2 the peak value is 2V and the RMS is \$\dfrac{2}{\sqrt{2}}\$ as its a sine wave.

A useful formula to know when adding two signals which do not share any frequencies in common is:

$$\text{RMS} = \sqrt{U1_{\text{RMS}}^2+U1_{\text{RMS}}^2} $$

Which in this case \$ RMS = \sqrt{4^2+\left( \dfrac{2}{\sqrt{2}}\right)^2} = \sqrt{18}\approx\ 4.243\$

The positive peak is just 4 + 2 = 6 V

The the minimum value is 4 - 2 = 2 V

So the peak to peak is 6 - 2 = 4 V as you would expect since adding a DC offset wont change the peak to peak.

Alternatively you can do this from first principles

$$RMS = \sqrt{\dfrac{1}{T} \cdot \int_0^T \left(U1(t)+U2(t)\right)^2dt}$$