Answer:
They need travel 3.7 miles to reach their goal.
Step-by-step explanation:
The total number of annual miles walked by the club corresponds to the sum of the 5 partial tours, that is:
Total Miles = 4.6 + 3.7 + 5.1 + 2.9 + X, where X represents the number of miles traveled on the last excursion. As you want to travel a total of 20 miles, you have:
Total Miles = 4.6 + 3.7 + 5.1 + 2.9 + X = 20
X = 20 - 4.6 - 3.7 - 5.1 - 2.9 [transposition of terms]
X = 3.7 miles to reach your annual 20 miles goal.