Answer:
Correct choice is D
Step-by-step explanation:
First second - 5 feet,
second second 5+7=12 feet,
third second 12+7=19 feet, i.e.
This rule represents the arithmetic sequence, where
[tex]a_1=5,\\ \\d=7.[/tex]
You actually have to find [tex]a_{15}[/tex] that can be calculated using formula:
[tex]a_n=a_1+(n-1)d.[/tex]
In your case,
[tex]a_{15}=5+(15-1)\cdot 7=5+14\cdot 7=5+98=103\ ft.[/tex]
Then the sum of first 15 terms of the arithmetic sequence is the distance Ms. Waara traveled.
The sum of n terms of the arithmetic sequence is
[tex]S_n=\dfrac{a_1+a_n}{2}\cdot n,[/tex]
that in your case takes look
[tex]S_{15}=\dfrac{5+103}{2}\cdot 15=810\ ft.[/tex]
