To calculate the frequency of red flowers in the garden, you can use the formula for frequency:
\[ \text{Frequency} = \frac{\text{Number of individuals with the trait}}{\text{Total number of individuals}} \]
In this case, the number of red flowers is 30, and the total number of flowers is 40.
\[ \text{Frequency of red flowers} = \frac{30}{40} = 0.75 \]
Therefore, the frequency of red flowers is 0.75.