I haven't looked at the other questions yet, but the first one is false
You're working with a probability density function. The probability of getting a value equal to 3, while working with a rv with pdf, is 0.a) i substituted in z=3 hence my answer was 0.112
What you're asked is the probability that the man fails to do it in 3 minutes. Which means it's the probability that it takes more than 3 minutes to do the task.
So you're looking for P(Z>3), which is , and not
I guess you made the same mistake for question b)