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