Answer: rms voltage is [tex]T_{rms}=2,33 V[/tex]
P = power
T = voltage
I = current
In a circuit you have that:
[tex]P_{peak} = T_{peak} * I_{peak}[/tex] (eq 1)
The rms value of a signal X is:
[tex]X_{rms}=X_{peak}/\sqrt(2)[/tex] (eq 2)
From eq 1, [tex]T_{peak} = 13 W / 3.9 A = 3,33 V[/tex]
Then, from eq 2, [tex]T_{rms} = 3,33 V / \sqrt(2) = 2,33 V[/tex]