Ihave a homework project in math and i don’t know how to do it can anybody ? i am really bad at math. it says 118/13=59/z then wants me to give it an answer ik the answer 6.5 but i just don’t know how to do it someone explain .

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?