Data Sufficiency

You're on track with the rate formula! The only extra step you'll need to do is some unit conversion:

Statement 1

We have no idea how fast Jim was driving - he could have gone 1 mile in 20 minutes or 20 miles in 20 minutes. Insufficient.

Statment 2

This is the opposite of Statement 1 - we don't know how long Jim drove for. He could have traveled at 30mph for 1 hour (giving 30 miles in total) or for 10 minutes (giving 5 miles in total). Insufficient.

Both

Now we have both rate (also known as speed or velocity) and time. This means we can use the rate formula (D=r*t) to find distance. HOWEVER, we have time in minutes, and rate in miles per hour. So to solve, we'll need to do some conversion to make sure our units cancel out. If Jim drives for 20 minutes, and there are 60 minutes in an hour, he drives for 1/3 of an hour. Let's plug that in:$$D=\frac{30\ miles}{hour}\cdot\frac{1}{3}hour$$ Then cancelling out hours:$$D=30\ miles\cdot\frac{1}{3}$$ $$D=10\ miles$$
So Jim travelled 10 miles from his home to the grocery store. Sufficient.