When 4 identical resistors and connected in series have a total resistance of 20 ohms and 2 amperes of current at the source, determine the potential difference across each bulb. DIAGRAM + CALCULATIONS
Your question starts with resistors....and finishes with bulbs....
FOUR resistors in series would all have the same current through them
v = i r
v = 2 (20/4) = 10 volts drop across each resistor