In this distance-time equation, both people are going in opposite directions. Because of this, we have to add the distances each traveled in order to find the distance between.
Both people have rates: Savannah is driving at 55 mph; Luke is driving at 62 mph.
Since the question states that they both drive for 3 hours, all we have to do is multiply both rates by 3.
55(3) + 62(3) = ?
Multiply:
165 + 186 = ?
Add:
165 + 186 = 351
After 3 hours, Savannah and Luke are 351 miles apart.
-T.B.