My last 10 points one more i swear lolz

Can someone me my sister? she is in third grade. 50 points and brainlist! ones that are not answered. plz and thx!

Me because some of question i don’t understand

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?