Balance length for a potentiometer circuit

[Bolter]

Homework Statement

Find value of balance length

Relevant Equations

V = kL

Here is the question itself

Here is my attempt at it

Does 4cm look right?

Any help would be great, thanks!

 

[kuruman]

That looks about right. You know that the voltage drop V_AB =15 V. To null the voltmeter you need a voltage V_CB = 6 V. Then $\dfrac{15~\mathrm{V}}{6~\mathrm{V}}=\dfrac{10~\mathrm{cm}}{L}~\rightarrow L=4~\mathrm{cm}.$