It’s a trick question. There is no speed you can travel the second mile and end up with a 30mph average over the two mile course. It’s impossible since you took 4 minutes to do the first mile.
You must travel the entire two miles in exactly four minutes to average 30mph.
Instant acceleration is not needed as it was stated as the max average speed the car could do for one mile up the hill.
This means it attained a speed faster than 15mph at some point on the uphill leg.
If I’m in a top fuel dragster,
and I do 100mph for one mile, and then I go 300mph for the second mile, what is the average MPH for a 2 mile trip ?
Which has absolutely nothing to do with average MPH.
Let's say that during the first mile, you went 5, then 10, then 15 mph, at each third of a mile. What would your average MPH for the mile course be? How long would it take? And what does it matter ? The answer you are working on is AVE MPH, not TIME.
If you are GIVEN MPH and DISTANCE, the outcome is 'time'. Therefore it cannot be the INPUT factor.