Answer:
The resistance of the original circuit is [tex]32\,\,\Omega[/tex]
Explanation:
In the original circuit, we have an unknown resistor that we call R, an unknown power supply that we call V, and the current is 15 Amps. in the second circuit with an added 8 Ω resistor in series, which gives an equivalent resistance of R+8 Ω, using the same power supply V, the current is 12 Amps. SO, we can write a system of two equations with two unknowns as follows:
[tex]V=R\,(15)\\V=(R+8)\,(12)\\then\\15\,R=12\,R+92\\3\,R=96\\R=\frac{96}{3} \,\Omega\\R=32\,\,\Omega[/tex]
