First you would have to know how many yards are in a mile. There are 1760 yards in one mile. which would mean that in 3 miles there are 5280 yards. then you would have to multiply 250 by 6 to get 1500. Take 1500 and subtract it from 5280 and you would get 3780 as your answer. He needs to go 3780 more yards to complete 3 miles. Hope this Helps.