Answer:
The total distance David has to travel 20 miles.
The speed limit is 30 mph. He leaves supermarket at 18 10 , he has 50 minutes to get home before 1900.
when traveling within the speed limit he can reach on time because he has to travel only 20 miles which is possible and it won't take him 1 hour according to the 30 mph speed limit.
1) The MST will have 3 connections to Mal, more than any other node.
2) The sum of weights is 250 +3*300 +500 = 1650.
.. (You can rule out 1560 as a choice because no weight ends in 10 or 60. This is simply test-taking savvy, not math.)