If you're looking for its length, it is 27 ft. If you're looking for its area, it is 189 ft squared.
Her home was 2 km 691 m from the store. (5 km = 5000m --> 5000-2309)
Nellie has to calculate the price per pound for every bag.
1) 2.52 / 3.5 = 0.72 $/lb
2) 5.40/7.5 = 0.72 $/lb
3) 7.92/11 = 0.72 $/lb
Then, price per pound is the same for any bag. There is no advantage of purchasing one or other, given that she can store any quantity.
You forgot the link to the page so we can answer it