Final answer:
Syd and David's average speed on their trip from California to Maine over two days was 50 mph.
Step-by-step explanation:
To calculate the average speed, we divide the total distance traveled by the total time taken. In this case, Syd and David drove 750 miles over a 15 hour period. So, the average speed is:
Average speed = Total distance / Total time
Average speed = 750 miles / 15 hours
Average speed = 50 miles per hour
Therefore, the average speed at which they drove on these two days was 50 miles per hour (B).