Answer:
A) 200 units
Explanation:
mean daily demand = 20 calculators
standard deviation = 4 calculators
lead time = 9 days
z-critical value (for 95% in-stock probability) = 1.96
normal consumption during lead-time:
= mean demand × lead time
= 20 × 9
= 180 calculators
safety stock = z × SD × √L
           = 1.96 × 4 × √9
           = 1.96 × 4 × 3
           = 23.52 calculators
reorder point = normal consumption + safety stock
            = 180 + 23.52
            = 203.52 calculators