How to calculate sum of multiuple entries from one drop down field and order by specific employee chosen in a dropdown

How to calculate sum of multiuple entries from one drop down field and order by specific employee chosen in a dropdown.

Example:

Dropdown called Employee

I choose Employee A

Dropdown called Passport_Weight

I choose 3

Submit and now 3 shows as passport_weight in the view for Employee A

- I then renter again

Drop down called Employee

I choose Employee A

Dropdown called Passport_Weight

I choose 3

In the View I would like a column called Total_Weight = 6 for Employee A

calculate sum of two entries from a drop down field