This is a question from

OG12 (#68) and is pretty straightforward. You have not copied it correctly which is why it is stumping everyone.

The correct question states "At a certain instant in time, the number of cars, N,

traveling on a portion of a certain highway can be

estimated by the formula (as given)

where L is the number of lanes in the same direction,

d is the length of the portion of the highway, in feet,

and s is the average speed of the cars, in miles per

hour. Based on the formula, what is the estimated

number of cars traveling on a

1/2-mile portion of the

highway if the highway has 2 lanes in the same

direction and the average speed of the cars is 40

miles per hour? (5,280 feet = 1 mile)"

So the portion is 1/2 mile NOT 20 miles. And thus the correct answer is D, after just plugging in numbers and converting 1/2 mile to feet.