If (x+5) is a factor the equation will equal zero when x=-5 so
3(-5^2)+14(-5)+k=0
75-70+k=0
5+k=0
k=-5
About 50 miles. hope this helps!
The mean of n numbers is the sum of the numbers divided by n.
You have a mean score of 84 after taking 5 tests. Let x be the sum of scores.

You scored a total of 420 points on five tests.
You need to have a mean score of 85 after taking 6 tests. Let y be the score you need to obtain. Your total score on 6 tests is 420+y.

You need to score 90 points on the sixth test.