If a secondary voltage is given across a particular resistive load in a series of known resistive loads, multiply the voltage by the ratio of the total load to the measures load to get total voltage.
Example: You have a series of a 200 ohm resistor to a 100 ohm resistor. The votage measured across the 100 ohm is 2 volts. 200 + 100 = 300. 300 / 100 = 3. 2 X 3 = 6. Total Voltage in the circuit is 6V