The actual value of resistance $$R$$, shown in the figure is 30$$\Omega$$. This is measured in an experiment as shown using the standard formula $$R = \frac{V}{I}$$, where V and I are the readings of the voltmeter and ammeter, respectively. If the measured value of $$R$$ is 5% less, then the internal resistance of the voltmeter is:

$$R' = R - 5\% \text{ of } R = 30 - 0.05 \times 30 = 28.5\ \Omega$$

The voltmeter is connected in parallel with $$R$$. Thus, the measured resistance is the equivalent resistance of $$R$$ and the voltmeter resistance ($$R_V$$):

$$R' = \frac{R \cdot R_V}{R + R_V}$$

$$28.5 = \frac{30 \cdot R_V}{30 + R_V}$$

$$28.5(30 + R_V) = 30 \cdot R_V \implies 855 + 28.5R_V = 30R_V$$

$$1.5R_V = 855 \implies R_V = \frac{855}{1.5} = 570\ \Omega$$