Answer:
3 miles south from the observation deck to the picnic area, then 4 miles east from the picnic area to the lake and at last 3 miles north from the lake to the camsite.
Explanation:
Let us start from the end:
1. Vinnie hiked 3 miles north from the picnic area to the observation deck, then he hiked 3 miles south from the observation deck to the picnic area.
2. Vinnie hiked 4 miles west from a lake to the picnic area, then he hiked 4 miles east from the picnic area to the lake.
3. Vinnie hiked 3 miles south from the campsite to the lake, then he hiked 3 miles north from the lake to the camsite.
Hence, if Vinnie wants to hike back, he should hike 3 miles south from the observation deck to the picnic area, then 4 miles east from the picnic area to the lake and at last 3 miles north from the lake to the camsite.