Answer: 18 miles west
Explanation:
The mall is west of the highway.
The hospital is then west of the mall.
If the hospital is west of the mall which is already to the west of the highway, the Hospital must be west of the highway as well.
The hospital is 12 miles west of the mall which is then 6 miles west of the highway. As they are both west, it is a continuous distance and we can simply add their distances up and assume the distance is linear.
The distance between the hospital and the highway is therefore:
= 12 + 6
= 18 miles west