50 mph for 3 hours = 150 miles
70mph for 2.5 hours = 140 + 35 = 175
175 miles - 150 miles = 25 miles
We have the formula to compute the probability of having exactly k successed over n trials, given a probability p of success (and implicitly a probability 1-p of failure), which is

Now, the probability of at least 3 successes is the union of the following event: exactly three successes,exactly four successes and exactly five successes.
We can compute their probability and sum them:
So, the answer is about 36.79%
Hey, I have already answered these all questions except the last question in your previous question. Make sure to see them.
For the last question, the answer would be the second choice as when times keep flowing, the distance still remains the same (not to be confused with speed.)
Basically when times keep going, the distance will stay the same without any changes.