A friend form work asked for my help but the book dosent give good examples, formula and answer would be great

Question

The Polo Development Firm is building a shopping center. It has informed renters that their rental spaces will be ready for occupancy in 19 months. If the expected time until the shopping center is completed is estimated to be 14 months with a standard deviation of 4 months, what is the probability that the renters will not be able to move in 19 months?

Answer 1

19 months - 14 months = 5 months
5 months / 4 months (s.d.) = 1.25 standard deviations

Look up 1.25 s.d. on the chart to get the percentage.