Help me i'm sorry for this much this is very important

Using pert, adam munson was able to determine that the expected project completion time for the construction of a pleasure yacht is 21 months, and the project variance is 4. a) what is the probability that the project will be completed in 17 months? b) what is the probability that the project will be completed in 20 months? c) what is the probability that the project will be completed in 23 months? d) what is the probability that the project will be completed in 25 months? e) what is the due date that yields a 95% chance of completion?

X/y + 4y/x divided by x/y - 2y/x explain as in depth as you can how you simplfied the fractions. i don't know where to start on this : /

Thirteen bowlers were asked what their score was on their last game. the scores are shown below 190,150,154,194,181,190,170,151,170,178,161,180 find the range of the bowlers score a.56 b.44 c.34 d.23