To calculate the relative humidity, you can use the formula:
\[ \text{Relative Humidity} = \left( \frac{\text{Actual Vapor Density}}{\text{Saturation Vapor Density}} \right) \times 100 \]
Given that the actual vapor density is 6 grams/cubic meter and the saturation vapor density at 30°C is 30 grams/cubic meter, you can substitute these values into the formula:
\[ \text{Relative Humidity} = \left( \frac{6 \text{ g/m}^3}{30 \text{ g/m}^3} \right) \times 100 \]
Calculating this gives:
\[ \text{Relative Humidity} = \left( \frac{6}{30} \right) \times 100 = 0.2 \times 100 = 20 \]
Therefore, the relative humidity is 20%.