To calculate the average speed of the car, you need to use the formula:
\[ \text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}} \]
In this case, the car travels 30 miles in \( \frac{3}{4} \) of an hour.
First, convert \( \frac{3}{4} \) of an hour to minutes:
\[ \frac{3}{4} \times 60 = 45 \text{ minutes} \]
Now, you can calculate the average speed:
\[ \text{Average Speed} = \frac{30 \text{ miles}}{45 \text{ minutes}} \]
To convert the time from minutes to hours:
\[ 45 \text{ minutes} = \frac{45}{60} \text{ hours} = \frac{3}{4} \text{ hours} \]
So, the average speed of the car is:
\[ \text{Average Speed} = \frac{30}{\frac{3}{4}} = 30 \times \frac{4}{3} = 40 \text{ miles per hour} \]
Therefore, the average speed of the car is 40 miles per hour.