Answer
The voltmeter reading is $~~4.86~V$
Work Step by Step
The equivalent resistance of $R$ and the ammeter is $88.0~\Omega$
We can find the equivalent resistance of $R$ and the ammeter, and the voltmeter, which are in parallel:
$\frac{1}{R_{eq}} = \frac{1}{88.0~\Omega}+ \frac{1}{300~\Omega}$
$R_{eq} = 68.0~\Omega$
The equivalent resistance of the circuit is then $168~\Omega$
We can find the total current in the circuit:
$i = \frac{12.0~V}{168~\Omega} = 71.4~mA$
We can find the potential difference across $R_0$:
$\Delta V = (71.4~mA)(100~\Omega) = 7.14~V$
Then the potential difference across the voltmeter is $12.0~V-7.14~V = 4.86~V$
The voltmeter reading is $~~4.86~V$
