Calculate Sums Based on Drop-Down Selection While Referencing Another Field

Hello,

I'm trying to calculate the sum for what is entered in Expense_Total_1, Expense_Total_2, etc. as it relates to a specific code in Accounting_Code_1, Accounting_Code_2, etc.

Say if '$8.50' is entered into Expense_Total_1 and '$10.00' Expense_Total_2, and '8280' is chosen from the drop-down in both  Accounting_Code_1 and Accounting_Code_2, then '$18.50' should be reflected in Total_Misc_Expenses.

I've attached a copy of the PDF to give a better view. Any and all help is greatly appreciated. Thank you in advance!