Answer:
219.57 units
Explanation:
Given :
Daily demand, d = 7 per day
Standard deviation, = 2 per day
Service probability = 98%
Total number of days per week = 7
Lead time , L = 3 days
On hand inventory, I = 35 
Now calculating the optimal order quantity by using the given formula,
 .............(i)
   .............(i)
First, we will find out the value of   and z.
 and z.
Therefore, 

         
        = 11.48
Now the value of z can be found out from the z-table,
Z value for 98% service level = 2.054
Now putting the value of  and z in equation (i), we get,
 and z in equation (i), we get,
 
  
    = (7)(30+3)+(2.054)(11.48) - 35
    = 231 + 23.57 - 35
    = 219.57 units
So the optimal number of the units required to be order = 219.57 units