-- I think we can all agree that the total resistance in the circuit is (20 + 60) = 80 ohms.
-- Since the 20-ohms is 1/4 of the total resistance, the 20-ohm resistor will have 1/4 of the total voltage across it. (This is one of the neat things about a series circuit.)
-- The total voltage is 120-volts.
-- 1/4 of the total voltage is 30 volts .
