Final answer:
The car's average speed for the trip is 28 km/h, which is not listed in the provided options. It is calculated by dividing the total distance travelled, 7 km, by the total time taken for the trip, which is 0.25 hours.
Step-by-step explanation:
To determine the average speed of the car for the trip, we must first calculate the total distance travelled and then divide that by the total time taken for the trip. The car travels 4 km east and then 3 km south, making a right-angled triangle with these two distances as the legs. However, for average speed, we are concerned with the total distance travelled, not the displacement.
The total distance traveled by the car is 4 km + 3 km = 7 km.
The total time of the trip is given as 15 minutes, which is equivalent to 0.25 hours since there are 60 minutes in an hour.
Now, we calculate the average speed using the formula: Average speed = Total distance / Total time.
Average speed = 7 km / 0.25 h = 28 km/h.
This option is not listed in the question, so it seems like there may have been an error in the provided options.