Let's restate the question, how many miles per day did Mr. Adams drive? When we see per we know it's a rate and we use fractions to solve. If you have a tough time with this think of MPH, or miles per hour also written m/h or Miles/hour.
We need to solve for miles/day. We know Mr Adams drove 151.2 miles in 24 days. Let's rewrite that as 151.2miles/24day
Now divide. 6.3 miles/day.