Weighted average Inventory Valuation

Please suggest me the appropriate inventory valuation model to achieve my objective.

for example if i purchase 10 qty @ 15 per unit and sell 6 qty out of that and then purchase another 16 qty @ 10 per unit, I am expecting an inventory value as below

inventory remaining out of first lot 4 qty *15 = 60

inventory of second lot 16 qty * 10 = 160

Total  value = 220

Inventory value per unit as on date , 220/20 =  11 per unit.

If i am using weighted average cost, i am sure that my inventory value per unit at this moment will be (10*15)+(16*10) = 310 divide by total qty (10+16), ie , 310/26 = 11.92.

i want inventory value of 11 per unit. which inventory valuation type will help me to achieve this?

Thanks in advance

Jomy George