Question

*R3= 9 ohms What is the voltage drop running through resistor five?

Answer 1

The correct answer is: The voltage drop across $R_5$ is 45V.

Explanation:
First you need to find the total current of the circuit, which is:
According to Ohm's law:

V = I * R

I = V/R --- (1)

Where
R = Total Equivalent resistance of the circuit
V = Total Voltage = 90V
I -= Total Current

First let us find the equivalent resistance:
$R = R_1 + R_2 + R_5 + \frac{R_3*R_4}{R_3+R_4} \\ R = 3 + 6 + 15 + \frac{9*18}{9+18} \\ R = 30$

Now plug in the values in (1):
(1) => I = 90/30 = 3A

Now that we have current of the circuit, we can now find the voltage drop across  $R_5$ = 15 ohms using:
$V_5 = I * R_5$

Where $V_5$ is the voltage drop across resistor 5;
$V_5 = 3 * 15 = 45V$