To calculate the frequency of red flowers, you can use the formula:
\[ \text{Frequency} = \frac{\text{Number of red flowers}}{\text{Total number of flowers}} \]
In this case, there are 30 red flowers out of a total of 40 flowers. So, the calculation would be:
\[ \text{Frequency of red flowers} = \frac{30}{40} = 0.75 \]
Therefore, the frequency of red flowers is 0.75.