t = 2.4 hours
Since travel time and average speed are inversely proportional, we can create a function where (time)(speed) = k, where k is some constant number. Since time is 3hrs and average speed is 65mph, and our new speed is 80mph, we can create a new equation since they are both equal to constant k.
Thus, since (65mph)(3h) = k and (80mph)(time) = k,
(65)(3) = (80)(t)
Then, using algebra, we solve for t and get
t = 2.4 hours
