Answer: 93 units should be ordered.
Step-by-step explanation:
Since we have given that
Standard deviation = 4
Average = 30 units
Number of weeks in order interval = 3
Desired service level = 97.5%
Number of units on hand = n = 43
So, the expected value would be
[tex]E[x]=30\times (3+1)+1.96\times 4\sqrt{3+1}-43\\\\E[x]=30\times 4+1.96\times 4\times 2-43\\\\E[x]=120+15.68-43\\\\E[x]=92.68\approx 93[/tex]
Hence, 93 units should be ordered.