Answer: D) 2x+19
Explanation:
Given : During a walkathon,
Total distance traveled by Team A = 6x+12 miles and
Total distance traveled by Team B = 4x-7 miles.
Now, the difference in miles between the two teams = Total distance traveled by Team A - Total distance traveled by Team B
[∵ (-)(-)=(+)]

Hence, the difference in miles between the two teams = 2x+19
Thus , the correct answer is D) 2x+19 .