Answer:
L = 2D + 54
132 miles
Explanation:
Starting length: 54
Additional length each day: 2
On day 0, the additional length is 0.
On day 1, the additional length is 2 × 1
On day 2, the additional length is 2 × 2
On day 3, the additional length is 2 × 3
...
On day D, the additional length is 2 × D or simply 2D.
The total length after D days is the original length plus the total amount of the daily additions.
The equation is:
L = 2D + 54
On day 39, D = 39
L = 2D + 54
L = 2 × 39 + 54
L = 78 + 54
L = 132
Answer:
L = 2D + 54
132 miles