Question 960771
5/400 = x/640
x = 640 * 5 / 400
x = 8
it would take 8 hours.


alternatively,
r*t = d
r = rate
t = time
d = distance
with t = 4 and d = 400, you get r = 400/5 = 80 miles per hour.
at 80 miles per hour, it would take 640 / 80 = 8 hours.