$$Average\ speed\ =\ \frac{dis\tan ce}{time}$$
Distance = speed * time
Statement 1: Jim leaves home at 9:00 a.m. and arrives at the supermarket 20 minutes later, driving nonstop.
Therefore, the total time taken = 20 minutes or 0.33 hour.
But the speed is unknown, hence, statement 1 is NOT SUFFICIENT.

Statement 2: During this trip, Jim drives at an average of 30 mph.
The time taken is unknown, hence, statement 2 is NOT SUFFICIENT.

Combining both statements together:
Time taken = 0.33 hour
Average speed = 30 mph
Total distance = speed * time = 30 * 0.33
= 9.9 miles
Conclusively, both statements are SUFFICIENT.

Answer = option C