Can someone please help answer this! bs answers will be prosecuted!!!

Question 5 spring semester final exam math evaluate

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?

Whats are the trickiest steps to do when adding or subtracting rational expressions? how does knowledge of rational numbers u in adding and subtracting rational expressions?