It's really difficult to make out the circuit above. Quite frankly, your
question leaves me to wonder how far 'above' it may be.
The best I can do will be to try and fabricate an answer based on the
information given in the text of the question, augmented only by my own
training, chutzpah, and life experiences.
If the circuit ... wherever it is ... consists entirely of the single 3-ohm
resistance and no other components, and the current through the
resistance is 10 Amperes, then
Voltage = (Current) x (resistance) = 30 volts .
