Answer:
The highest rms voltage will be 8.485 V
Step-by-step explanation:
For alternating electric current, rms (root means square) is equal to the value of the direct current that would produce the same average power dissipation in a resistive load
If the peak or maximum voltage should not exceed 12 V, then from the relationship

where
is the rms voltage
is the peak or maximum voltage
substituting values into the equation, we'll have
= 8.485 V