For motion at constant speed, there is a direct relationship between distance (d), speed (v), and time (t):
d = vt
The information in the first sentence allows us to calculate the constant speed v, since it gives us distance traveled over a certain time. Specifically:
80 miles = v*(2.5 hours) --> v = 80 miles/2.5 hours --> v = 32 miles/hour.
In the last sentence, we are given a new distance d' = 270 miles, and are asked to calculate t', the new time in hours, now knowing that v = 32 miles/hour. This just involves using the first equation above again, and solving for t' knowing d' and v.
Hope this helps, Nancy!